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Buck Nelson
(Colter) - MLife

Locale: Alaska
Giardia: Let's Talk SCIENCE on 09/13/2012 06:54:13 MDT Print View

It's interesting to me what a heated topic this can be, and how much misinformation is out there.

Most of us have read that there is little scientific evidence showing that waterborne giardia transmission is happening in the backcountry.

Actually, there is a great deal of scientific evidence for waterborne transmission.

Giardiasis as a threat to backpackers in the United States: a survey of state health departments contains this statement: Thus, neither health department surveillance nor the medical literature support the widely held perception that giardiasis is a significant risk to backpackers in the United States. In some respects, this situation resembles that recently described by Campbell and Smith in reference to shark attacks [18]: an extraordinarily rare event to which the public and the press have seemingly devoted inappropriate attention.

That paper, perhaps more than any other, has misled people about what the science really says. I have spent a lot of time debunking that paper
which I hope you'll read, here.

This is one of the last bastions of reason and (usually) civility on the internet. I'd like feedback on my conclusions, and would like to stick to the science and try to avoid the standard "I've never had it so it can't be that big of a problem" vs "I have had it, and it definitely is" and "liar, liar pants on fire" kind of thing.

Rick Dreher
(halfturbo) - MLife

Locale: Northernish California
Re: Giardia: Let's Talk SCIENCE on 09/13/2012 10:50:01 MDT Print View

Hi Bruce,

Hving ridden on the same merry-go-round myself I try not to get trapped in the futile pursuit of a definitive answer to the question of whether my source water is contaminated--none exists. The shark attack metaphor is a canard (hey, that's a mixed metaphor right there) because if you've been attacked by a dang shark you dang well know it. By contrast, if you've been exposed to giardia (or any of dozens of waterborne pathogens) you 1. don't know it at the time, 2. may remain asymptomatic and never know it, 3. may become ill after a time but never receive a definitive diagnosis or, if diagnosed, are unlikely to know where or how you contracted it.

So the proper science to apply is not microbiology, it's risk assessment—instead of summoning a microbiologist, seek an actuary. The vast array of portable treatment technology exists gives us the means to reduce our exposure to waterborne pathogens, relatively easily. The decision rests with us whether to treat. If you think water is safe, you collect and drink it. If you think the water could be "contaminated," then you filter/treat. The cautionary tale most folks with a lot of backcountry time in have, is the unfortunate shock of discoving their presumably pristine water actually has a stomach-churning contamination source (such as an upstream animal carcass or cattle bog) in seemingly safe waters.

Today's water treatment is mostly quite easy and adds a layer of protection. To use it or not is similar to clicking in a car's seatbelt--there it is, why not use it? One argument I've yet to hear is "If I do that I'll feel TOO safe."

As a sidebar, we didn't even know giardia was a pathogen until the 20th century, yet it was discovered by Van Leeuwenhoek in the 17th. Cryptosporidium wasn't commonly discussed until major, citywide outbreaks sickened thousands. To drag sharks back in, they travel and a safe beach today may be a great white snackbar tomorrow. Likewise, a safe creek today may host a dead moose next spring. Lacking fieldborne test equipment, how does one manage their personal risk making their treatment decision?

Cheers,

Rick

Buck Nelson
(Colter) - MLife

Locale: Alaska
What Rick said on 09/13/2012 11:45:14 MDT Print View

That was one of the best, most insightful posts I've seen on the topic.

I think step one in risk assessment is to identify the hazards. The two most well-known authors on the topic are probably Welch and Rockwell. They both use the shark attack analogy. They both say that medical literature does not show it is a significant risk. People believe that stuff. I've seen it quoted over and over. It's easy to prove they are wrong. If we don't know that water is a hazard when it comes to giardia, there's no way to make a rational risk assessment.

That's why I wrote the rebuttal directed at that paper. No one has yet made a serious effort to debunk it. If it can't be rationally debunked, presumably the science shows waterborne giardiasis IS a significant hazard and perhaps new risk assessment might be appropriate.

Tom Lyons
(towaly) - F

Locale: Smoky Mtns.
I automatically treat. on 09/13/2012 11:51:22 MDT Print View

Any time I am drinking unknown water, I treat it.
My typical method is chlorine bleach, time, and an activated carbon filter to get most of the chlorine out before I drink it.

It doesn't take all that long to treat it, and it works very well from my experience.
And my experience is fairly extensive, considering that ALL my drinking water for 14 years comes from an open surface stream in the woods of the Tennessee foothills, which I treat myself and drink as my normal home water supply.
And I have never gotten any sickness from it. And believe me, those woods are FULL of critters of all types.

I pump it into a food-grade barrel from the stream, chlorine treat it, and then pump it thru a carbon block filter into the house.
In all cases that I have encountered, 20 minutes in the chlorine was all that was necessary. I treat it after the water clears all the sediment to the bottom, and then 20 minutes after treating, I consider it ready.

Dena Kelley
(EagleRiverDee) - M

Locale: Eagle River, Alaska
RE Giardia: Let's Talk SCIENCE on 09/13/2012 12:11:36 MDT Print View

I get amused at the arguments that ensue over this topic. I don't tell other people what they ought to do- I've been out with people that drank straight from the stream and more power to them. I boil my water. I do have chemicals in my kit for just-in-case but I'm not a fan of chemicals in my water and boiling works for me. I boil at dinner so I have hot water bottles for my sleeping bag which gives me water for breakfast and then I boil at breakfast for water for the rest of the day. That works fine for me. I'd rather be safe than sorry, personally, but I figure everyone I hike with is a grown up and if they want to chemically treat, filter, boil or not treat at all...that's their business.

Stephen Barber
(grampa) - MLife

Locale: SoCal
I'm with Rick on 09/13/2012 12:36:22 MDT Print View

Risk assessment is indeed the proper approach; and seat belts/airbags the analogy.

I've been treating my water since way back, for decades with iodine crystals (yeah, I'm really a meth manufacturer [snarky joke] - sorry, but the Feds taking out the easiest source or crystal iodine treatment still irritates me!). Today I use a Steripen and enjoy the better tasting water and more efficient destruction of any possible nasties.

Buck Nelson
(Colter) - MLife

Locale: Alaska
What I'm trying to get at... on 09/13/2012 12:37:46 MDT Print View

is the underlying science. What has the published science (vs our opinions) shown? Did you think my analysis (Post #1) stands up to scrutiny?

Tom Lyons
(towaly) - F

Locale: Smoky Mtns.
Re: What I'm trying to get at... on 09/13/2012 12:53:03 MDT Print View

If you are essentially stating that there is a risk of giardiasis when drinking from unknown water sources that aren't purified, then yes, I think you are accurate and could be defended.

The other side of the coin is that there is a chance you won't get it, too.
As they said above, risk analysis is the "middle ground".


As I stated, I always treat before drinking.
Others don't.
Everybody takes their risks.
Being "absolutist" on any matter is very difficult.
FWIW, I am in agreement that there is enough risk to warrant treatment of unknown water sources.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Risk Assessment on 09/13/2012 13:05:58 MDT Print View

I just looked it up and there are about 16 shark attacks per year in the U.S. According to a newpaper quote one physician in Mammoth Lakes said they get several cases per week of backpacker giardiasis. There are likely tens of thousands of cases in the U.S. It is nothing like the likelihood of shark attack.

There are about 40,000 auto fatalies per year in this country, and millions of lesser accidents. That's why I wear my seat belt. If there were only 4 fatalities a year, I wouldn't. I need to know if it's 40,000 or 4. That's why I'm trying to get at the underlying science which will help determine the odds to begin with. If science shows no one is getting waterborne giardiasis we don't need to wear our seat belts so to speak.

There are lots of valid opinions here but we are largely rehashing old and familiar ground. Does anyone have any specific comments on my blog post which discusses the underlying science?

Thanks!

David K
(aviddk) - F

Locale: SW Oregon
Science it's right here on 09/13/2012 16:31:07 MDT Print View

If you want answers about Giardia they would be in this book. The $279 price tag may deter the casual reader. I hate to admit that I actually have read this book, but that was more than ten years ago.

http://www.amazon.com/Giardia-Giardiasis-Biology-Pathogenesis-Epidemiology/dp/0306415399

Katy Anderson
(KatyAnderson) - F
Thanks on 09/13/2012 16:51:02 MDT Print View

Bruce, I really appreciate your efforts to shine some light and science on the giardia question. What others have said, that this is a question of risk assessment, strikes me as very true. As you so correctly point out, all we need now are some hard facts about the safety of the water and the science of giardia infection so that we can each make that risk assessment.

I see two ways of assessing the risk of drinking untreated water: test the water or study the impact of drinking untreated water.

Testing the water:
The problem with this approach is that any government or private entity that tested the water and declared it free of infectious agents would put themselves up for a huge liability risk. So it is not done.

New studies on hikers drinking untreated water:
The studies that you've found looking at groups of backpackers and campers that drank unfiltered water are from the 1970s. That makes sense as this was before modern water filters. I'm thinking at that time the only option for effectively treating for giardia was boiling all drinking water. Some people boiled, others didn't bother, and it was fairly straight forward to compare the two groups. It would be great to see newer studies and updates to that 40 year old data. Today the vast majority of backpackers follow the standard recommendation to treat all their drinking water. So setting up a study comparing infection rates for those who drink untreated versus treated water is no longer a simple matter. That's why we don't have any modern giardia studies.

Bottom line, there is no modern data, no recent studies, not much science at all to go by.

So instead of science and data we make our own individual risk assessments based on experience. You got infected so you treat the water, I never have so I continue to drink untreated. Neither of us is right or wrong, just making different choices.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Giardia: Let's Talk SCIENCE on 09/13/2012 16:58:04 MDT Print View

OK, some comments.

> Most of us have read that there is little scientific evidence showing that
> waterborne giardia transmission is happening in the backcountry.
> Actually, there is a great deal of scientific evidence for waterborne transmission.
Straw man here. I think the first sentence is false in itself. What most may have read is that there is little scientific evidence for *significant amounts* of waterborn transmission.

Now, medical and hospital statistics. These cannot be relied upon very much. The typical case is that someone presents to a GP or a hospital saying that they got sick while backpacking, or possibly complaining of giardiasis, so they are treated for giardiasis and subsequently get better. Another count for the records. Case closed? No way. First of all, very rarely is the patient actually tested for the presence of giardia cysts. So why did they get better after treatment? Because the real infection simply ran its course and disappeared.

To compound the above, the incubation time for giardiasis is about 10 days. So none of those people who come back from the backcountry *already sick* are likely to have giardiasis. In most cases they probably have gastro, and in most cases that will have happened via the toilet-hand-mouth route. And a gastro infection is fairly short lived. But it seems this delay gets ignored by a lot of GPs and hospitals. (Give the guy a Flagyl pill and next case please.)

It's when someone complains of feeling sick several weeks after coming home that you might consider giardiasis. But that is not going to cover a hospital in a populat mountain region. The person will have gone home by then.

Am I discounting giardiasis entirely? No way. Giardiasis can happen. But *proven* cases are not that common. (Microscope examination is required.) We know there are localised hot-spots for giardia cyst contamination and significant numbers of infection cases do happen there. Typically, these hot spots are very popular camping sites where toilet behaviour is 'sub-optimal'. I can name some places myself. But animal vectors do also exist (beavers, foxes, etc).

What usually gets ignored a lot is the effect of dilution. Suppose a bit of infected fecal matter gets into a creek. How many cysts will be around 24 hours later, assuming the creek has normal flow? Very, very few! The same argument applies to E coli bacteria of course. When you wash your hands, most of what you are really doing is diluting any contamination that might be on your hands. It works.

Should you treat your water? At one stage the 5 million plus residents of Sydney (Australia) had to boil their water for a week to avoid a Crypto outbreak in the City water supply (caused by cost-cutting by Sydney Water). You were safer drinking mountain water for a while. On the other hand, some mountain streams near Sydney are still hopelessly contaminated by drainage from houses: we don't like touching the water in those streams.

I have (as most will know) a range of water treatment methods available to me. Mostly I use UV Steripen IF needed, but these days we focus more on carefully selecting our water source. We are just back from 2 months walking in the European Alps, where there are a lot of cows, sheep, goats, and wild animals. We did not take any water treatment gear; we did not get sick either.

Assessing the risk of any water-borne infection is really an exercise in statistics. You multiply the single-case danger by the probability of that danger. We KNOW that humans are extremely poor at doing this (which partly explains why people gamble or buy lottery tickets).

But, it's a free world.
Cheers

Paul Johnson
(johncooper) - F

Locale: SoCal
Re: Risk Assessment on 09/13/2012 17:19:58 MDT Print View

+1 to Rick Dreher. This is a well written view of what I practice.

In an effort to stay within the OP question and the most recent post.

"My conclusion: Giardiasis as a threat to backpackers in the United States: a survey of state health departments is deeply flawed and misleading for the reasons outlined. For backpackers, there is more scientific evidence to support the spread of Giardiasis through water than there is through hygiene. That said, there is good scientific evidence that hygiene plays a significant role in gastrointestinal health for outdoors people"

I agree the with your conclusion that the Welch paper is flawed and Welch fails to prove his conclusion. I disagree with your conclusion that the cited references establish "...there is more scientific evidence to support the spread of Giardiasis through water than there is through hygiene." The reports you cite, simply don't address the conclusion. For example the "Giardiasis in Colorado: an epidemiologic study" cites an increase due to drinking untreated water, but doesn't have any data regarding hygiene. You could infer 38% versus 18% increase in Giardia due to camping overnight is due to poor hygiene, but this isn't stated. You have to be careful regarding the 50% versus 18% comparison for those drinking untreated water. There is likely a significant overlap with those that camped overnight and those drinking untreated water. For this reason, we can't determine whether the Giardia was due to camping overnight or drinking untreated water.

Part of my reasoning for citing the above is to answer your most recent post regarding the underlying science. These reports have neither the data to confirm or disprove conclusions regarding the overall risk of Giardia when backbacking nor data comparing hygiene versus untreated drinking water as the source of transmission.

As noted above, Rick Dreher captured my beliefs in risk assessment. I use the following as my "actuary" for the sierras. http://www.highsierrahikers.org/Derlet-and-Carlson-2006.pdf. This report also changed my behavior to be particularly careful at water sources near stock trails. I find this approach to be the most data driven.

Brian UL
(MAYNARD76)

Locale: New England
Re: Giardia: Let's Talk SCIENCE on 09/13/2012 17:22:22 MDT Print View

I don't have any confidence that any legitimate scientific long term studies have been done that address backpackers and the water sources they use. It defiantly can't account for a backpacker who is careful about their water sources and uses small seeps and springs.
I can imagine some scientist simply going to ponds, rivers, lakes and scooping up water to test. I don't see them looking for seeps and springs in the mountains. That adds even more variables to these IMHO unreliable test.
We are left with nothing but conjecture when it come to backcountry water, n-1 personal experiences are all that we really have, and even then some people are for sure, better at judging what water sources are safe to drink from than others.
Water treatment cost money and time and is simply more stuff that needs to be manufactured marketed and disposed of so its not really that easy to decide to us it all the time. At the end of the day its still just HYOH

David K
(aviddk) - F

Locale: SW Oregon
Re: Re: Giardia: Let's Talk SCIENCE on 09/13/2012 18:17:14 MDT Print View

"3. may become ill after a time but never receive a definitive diagnosis or, if diagnosed, "

This is why I read the aforementioned book. I worked for Federal Land Management agencies and as a fly fishing guide starting in the early 70s. During that era everyone drank from almost any water source including dipping cups into major rivers without any thought of water treatment. I know people who were sick with undiagnosed health issues including crippling arthritis. Some thought they had chronic giardiaisis. At that time the best drug to treat the problem, Tinidazole, wasn't available in the United States. I know people who tried multiple courses of flagyl (Metronadiazole), which was the only drug used at that time, to no avail. Some went to Mexico and Canada to get Tinidazole (since 2004 available in the US). At one time I was even talking with a SoCAl medical student who was in the same medical quandary. Sick and unsure if he was infected or not. If he was infected he wondered what could he do about it.

One of the issues with giardia is the way you diagnose the illness. Stool samples are examined for the trophozoites or its cyst. The supposed gold standard used to require a series of three stool samples. Even in known cases sometimes the parasite didn't show up in stool samples, even after many, many samples.

If I remember correctly Giardia can move into the bile ducts and make a permanent home and never show up in stool samples. It also can become a chronic and incurable problem in some.

I think the old aporhism-- An Ounce of Prevention is Worth a Pound of Cure, applies here.

John S.
(jshann) - F
Re: Giardia: Let's Talk SCIENCE on 09/13/2012 20:05:06 MDT Print View

http://www.cdph.ca.gov/HealthInfo/Documents/Reportable_Diseases_Conditions.pdf

It's reportable by law in California like in most states. It appears the cases are to be reported to the local health officer for the jurisdiction where the patient resides, not at the location you are treated.

"It shall be the duty of every health care provider, knowing of or in attendance on a case or suspected case of any of the diseases or condition listed below, to report to the local health officer for the juridiction where the patient resides. Where no health care provider is in attendance, any individual having knowledge of a person who is suspected to be suffering from one of the diseases or conditions listed below may make such a report to the local health officer for the jurisdiction where the patient resides."

(guess they don't know they have a typo in their file)

Edited by jshann on 09/13/2012 20:08:45 MDT.

Stephen Barber
(grampa) - MLife

Locale: SoCal
Science and Giardia on 09/13/2012 20:49:12 MDT Print View

Giardia and backpackers is a difficult subject to do good scientific research. It's about a disease which is socially embarrassing, difficult to easily and accurately diagnose, and will often run its course if left untreated. Additionally many people will be carriers rather than obviously effected.

The best research for backpackers would be something like the Derlet and Carlson study on colliforms in Sierra waterways, but focusing on giardia instead (or giardia and crypto, or ?). Measuring the number of G. lambdis cysts found per gallon of water in a random sample of streams in a particular area would give you a good idea of the degree of contamination in that area. The problem is that any particular stream, of any minute size, may be more contaminated than another in the same area, due to the presence of contaminated f3c3s in contact with water upstream. Presumably the concentration would be diluted as more pure water entered the waterway, or increased if there were more contaminated f3c3s downstream. Thus an area could be said to be fairly low in contamination, but you drink from a particular streamlet and come down with a massive case of giardia cause a contaminate mammal p00ped upstream just before you drank.

Still having the general area contamination rates, recently checked, would help in risk assessment, but would be no guarantee of purity.



BTW, I was using crystal iodine back in the 70s, purchased from the local drugstore, so boiling was NOT the only method available back in the the early 70s.

Mark Fowler
(KramRelwof) - MLife

Locale: Namadgi
The risk is time variable on 09/14/2012 02:49:14 MDT Print View

One of the great problems in having a study that people seem to want, is that the risk varies with time. What may be very low risk water after the winter may become high risk after a busy summer season when flow levels drop, temperatures increase and the dump load is high.

You cannot sign off a stream as low risk because it was on the day you tested it, because you cannot guarantee that a person/animal will not contaminate it the next. Because of this, if I was a land manager I would never claim that any untreated water was safe to drink.

We "know" that some level of risk of infection is always present with untreated water. You, as a sensible person can judge whether you accept the risk or treat the water - either way it is your call. This becomes a more serious problem if you have responsibility for kids or neophyte walkers.

For my part, I choose my water carefully and treat if I am not totally happy with the source.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Giardia testing, incubation period, empirical treatment on 09/15/2012 05:37:33 MDT Print View

Hi Roger,

Here's a direct quote from Welch followed by what I said many of us have read. Since mine was a general statement and I wasn't quoting Welch it certainly isn't false or setting up a straw man.

"the evidence for an association between drinking backcountry water and acquiring giardiasis is minimal"

"Most of us have read that there is little scientific evidence showing that waterborne giardia transmission is happening in the backcountry"

You are right in saying hospital data cannot be relied upon. 90%+ of cases are not reported in the U.S. (and John, it is as you say required to report it in California and other places. As a rule usually broken it projects a distorted view of the extent of the problem.)

The incubation period is 3-25 days. I think that's a more useful number than about 10 days although a week to 10 days is about average.

I disagree when you say "very rarely is the patient actually tested for the presence of giardia cysts." It is one of those debating points that doesn't reflect the real world. Check out these two polls:

http://forums.outdoorsdirectory.com/showthread.php/94691-Giardia-Poll-Please-vote!

http://forums.backpacker.com/cgi-bin/forums/ikonboard.cgi?act=ST;f=914107219;t=9991159948

It is more accurate to say "often backpackers aren't tested before being empirically treated." For physicians who deal with giardiasis that often make sense. It can take several tests to confirm with the patient suffering for days waiting for results.

Undoubtedly some people are needlessly treated just in case, but most victims aren't treated at all and don't realize they have it. They are asymptomatic carriers.

I think your point about dilution is very important, and it works both ways. A creek crossing that's risky might be relatively safe in a few days of flowing, and one that's just been tested and shown to be safe can be instantly fouled. That's one reason I've argued that taking decades old numbers from the Sierra and extrapolating them to the rest of the world as it is now is worse than useless.

I also agree that people are often very poor at evaluating risk vs reward.

Paul McLaughlin
(paul) - MLife
Re: Science and Giardia on 09/15/2012 14:40:41 MDT Print View

It seems to me there are two studies that would need to be done to provide a reasonably scientific basis for the assessment of the risk of getting Giardiasis in a particular area:
1) A study of the water sources to measure the actual incidence of Giardia cysts in the water. As has been pointed out, this sort of study has the major issue of being out of date even before it is complete, as the concentrations (or lack thereof) are likely to change rapidly and essentially at random.
2) A concurrent study of backcountry travelers to asses both the incidence of Giardiasis and the incidence of asymptomatic infections. Concurrence is critical, as only with concurrent studies would you be studying subjects who have actually consumed the water you have tested, given the changeable nature of the water sources and the levels of contamination.

With these two studies in hand, we would be able to at least correlate the rates of infection with the levels of use, which seems like it would be useful, at least to some extent. We would not have any assurance that a particular source could be safely regarded as pristine, since that source might become contaminated at any time.

Absent these, it seems to me that we have almost no scientific basis to assess the risk of contracting Giardiasis from any particular water source. What we do have is the basic facts about the organism: it is spread by mammals and by being carried along by the streams and rivers in which it is deposited. Thus the seat of the pants method of assessing risk - i.e., "if this lake is frequented by people and horses and beavers the chances are a lot higher that it is contaminated with Giardia than that lake over there which is rarely visited by people, never by pack stock or livestock, and lacks the vegetation around it that would suggest beavers would visit it", and "if I see the snowmelt stream coming out of the snowbank I'm drinking it straight" - is pretty much the best we have.

I've had Giardiasis twice - both times contracted in foreign lands - and it aint' fun. So I'm reasonably careful - using the seat of the pants method I describe - about choosing which water I filter and which I don't. So far my method works for me, and has for 40 years, but of course I do not know whether I have cleverly avoided infection, am just lucky, or am asymptomatic.

It's all a crapshoot.

Dave U
(FamilyGuy) - F

Locale: Rockies
Re: Re: Science and Giardia on 09/15/2012 14:46:17 MDT Print View

"It's all a crapshoot."

No pun intended....

Harald Hope
(hhope) - M

Locale: East Bay
the science on 09/15/2012 18:48:31 MDT Print View

Someone asked me a question that made me think of the science of giardia yesterday, or the day before, so I read up on all the government pdfs and pages.

I wish I'd seen this thread, so I could post all the urls for the pdf stuff I read, cdc etc, but the overall thing that all the real sources agreed on were simple:

backpacking is a key infection vector, or activity. All sources mentioned it specifically, without exception.

The reports and articles all stated that 1 cyst is all that is required. Something like 1 to 10 cysts per liter can be expected in running water (assuming infected matter upstream or in your area), that's a number all the sources seem agreed on, and would account for the dilution factor. I kept looking for that 10 cyst ingestion requirement number I've seen referenced in backpacking sources like bpl, but not one of the gov webpages or papers mentioned that higher count of 10 being required, in fact, the only place I saw it mentioned was places like bpl or other backpacking oriented information pages/sites. BPL is not a health science resource, so I don't care what people believe or don't believe, but if that's a myth, it should be terminated and stopped before people get hurt.

One page was kind of interesting, and was discussing why beavers were associated with it, and it noted that association was almost always caused by beavers being close to campgrounds, and getting infected by campers, then their fe ces contaminates the water, and so on.

The notion I come across that one can 'see' if water is good or not good struck me as particularly fantasy based, if there is some fecal matter in the water upstream from where you are, it's not good, and you certainly cannot see that fact, or smell it, maybe you can intuit it if you have a particularly excellent connection with nature and it's flows and patterns, but for average use, you certainly cannot do any such thing.

Again, I wish I'd seen this thread, I'd post every article I read, but they really seemed to agree in general. The two vectors were water and spread fe ces, which actually explains the observation that people make about handling other backpacker's food and getting giardia after that, that fits exactly, poor sanitary habits, then touching the food, then you touching it certainly could spread it, and that seems to be a very common vector.

The thing I was looking for, as scientific fact, not speculation, was specifically, how long giardia cysts can live out of the water, when it's dry. What confuses that question is a common fector, fe ces on doorknobs, trailmix etc, in trace amounts, which I guess lets giardia move to your body. I didn't find anywhere that told me that, but I did find some interesting stuff about temperature and cyst survival, in water, it's a few months when cooler, but drops steadily when warmer, if i remember right, 54C water they lived only 10 minutes, for example, boiling water I believe killed them almost immediately.

I just footnote this by observing that the cdc does not have a wonderful track record, and often lags behind the times, but they lag from what I have seen in underestimating, not overestimating, risk factors. Every single government document listed backpacking specifically as a source of infections, without exception.

This fits nicely with what Edward Abbey noted many years ago in Desert Solitaire, when he observed that prior to 1965 (or was it 1955? been a long time since I read it) or so, every free flowing water source in the USA was drinkable, talking about streams and so on, not of course rivers that flow through farming and urban areas. It took only some 10 years for that situation to change, due to live stock grazing on leased national park lands and backpackers practicing poor sanitation. Since we can read long threads covering people's experiences with that poor sanitation, ie, toilet paper on trails, non buried or inadequately buried waste, I'd certainly consider that to be a primary vector at this point, along with animals also spreading it.

So my quest for the science of it showed almost no variation in the data or information, and all of it said the same thing. Where exactly is the alleged 'science' going on that is disproving categorically the cdc and other government findings, making for an actual scientific disagreement? It's just one guy, right, who publishes some stuff online, correct? Typical internet stuff, right? Or is there real science going on somewhere?

As correctly noted in the sources, you can't test a stream for good or bad status, it's good when there's no contaminated fe ces upstream, and bad when there is. The beaver thing above mentioned that issue directly, and it's kind of obvious anyway, in cooler water giardia cysts only lived some 2 months max. Cysts floating in the water have no smell or flavor. Heavily contaminated water of course would be suspect as dirty, but water being clean shows you almost nothing.

This is why I carry a real filter, mechanical. What one paper explicitly stated was that bleach, chlorine, does NOT kill giardia, that's why people use aquamira, it's a tweaked bleach, so it would be good for that myth to be terminated once and for all, bleach does not kill giardia, unless the science is wrong, their outsides are too tough. Bleach could be a good option post filtering however, to kill smaller things, that's probably a good idea in very bad water.

Speaking for myself, I don't care what people do, but since I do somewhat try to follow the science of such matters, I'm not into pointless risks (for example, if I am carrying a filter already, why would I not use it? Sawyer squeeze is light and leaves no taste behind) when it comes to contracting long term weird parasite stuff, it's really not fun, trust me.

You can find all the cdc and other gov stuff easily, just google giardia and pick the authority sites, read the pdfs, etc. Maybe there's some other science out there, could well be, but that would be in scientific journals and medical journals, which usually are not free to read.

By the way, the bpl word filter really needs to be updated, it's kind of silly, this is an adult oriented site, grownups can handle the word fe ces.

Edited by hhope on 09/15/2012 18:59:10 MDT.

John S.
(jshann) - F
Re: the science on 09/15/2012 19:37:33 MDT Print View

"The thing I was looking for, as scientific fact, not speculation, was specifically, how long giardia cysts can live out of the water, when it's dry."

From Rockwell's paper
"Cysts can survive for as long as 2 to 3 months in cold water, but they cannot tolerate drying or freezing.12, 13, 15, 16, 17, 18 They are also destroyed by UV radiation, heat and biocides such as bleach.15"

"How many cysts does it take to get the disease? Theoretically, only one. But there are no documented cases of giardiasis being contracted from such low levels.8 Volunteer studies have shown that 10 or more are required to have a reasonable probability of it, with about one-third of persons ingesting 10 – 25 cysts getting detectable cysts in their stools.9, 10, 11, 13, 41, 42"

Edited by jshann on 09/15/2012 19:39:40 MDT.

Harald Hope
(hhope) - M

Locale: East Bay
not science, not peer reviewed on 09/15/2012 20:08:58 MDT Print View

That's just a guy, talking about one area, that he likes to hike in. It's not science, even though he's a scientist.

Can be good to start a conversation though, I'd certainly not follow anything he says beyond that.

I can point you to countless scientists writing outside their fields of expertise who say the darnedest stuff, doesn't mean it's wrong or right, but it's not technical science, it's not peer reviewed, science is sort of like a medieval guild system, has its rules and so on, and each discipline has its own methods and preferences.

The area he is right in, and in full agreement with the science, is that spreading via touch of contaminated materials is very likely.

I'm happy for people who do this practice and who can never get sick from water, I really am, but that's not science, it's just sort of anecdotal.

The CDC does not, as he suggests, take a 'very conservative stance', just follow their horrible record re Lyme disease, where they consistently have failed to take such a stance, nor does the general US system, which likes to err on the side of error, not caution.

I really wish this guy's paper would stop getting cited as some type of valid science, it's just an article he wrote. Can't we do a bit better? Plus, so he hikes in a few areas of the Sierras, and doesn't get sick, that proves exactly what, regarding other areas? Nothing. Maybe he's fond of high country, where most water is almost direct snow runoff, I don't know.

The thing of value though is to note that people are getting contaminated, and that they are spreading that contamination by touch.

I've read a lot of stuff on different topics over the past year, so the way data spreads is interesting to watch, but there's some common sense logic stuff that's not really happening with this guy, start here: is high country grazing leasing increasing, decreasing, or is it about the same? How about backpacker numbers? Higher, lower, or about the same? Science is VERY expensive to do, testing, etc, and it's very tedious, so it often takes a real kick in the pants to get it done, this guy Rockwell isn't doing it though.

to me the entire discussion is moot, it's a risk benefit thing, it costs me n othing to filter since I always will carry the filter, and if I carry it, I will use it.

The thing that does interest me however is another question, about using poison on living water, that to me is another matter altogether, there's hordes of good organisms in things we eat and drink, and poisoning them seems to be a very bad idea in terms of actually benefiting from being out there in the wilds, so I think in that sense I somewhat agree with Rockwell, drink the water as near fresh as you can manage, don't kill it. Giardia cysts are big and easy to filter out, so who cares if there are x or y infection rates, the Sierras are just one place, and the high sierras part of that place.

Humanity and its livestock are spreading, not shrinking, the ranges we occupy are increasing, not shrinking, the biosphere damage is getting worse, not better, to believe otherwise is to be somewhat oblivious to modern reality, so I bring a filter, it's easy and simple, I truly do not care what others do, nor do I care if people invent their own stories to make themselves happy. The sad thing is it would be so hard to actually do real science on this question, it would take years and even then it wouldn't be conclusive.

Some things in modern backpacking chit chat are fun to argue about, some to me there's no argument needed, this is definitely for me the latter category. But it's getting less and less likely real science will get done on this, we are running out of money and time, things are getting cut left and right, particularly in California, that will include various testing and regulatory bodies.

I also believe, by the way, that certain people if they do what they have always done tend to avoid problems, and are somewhat justified to note that it works for them. The idea is simple, ride a bike your whole life, no accident, get in a car, bang, you're not in the same groove, not following the same way.

Anyway, I just wanted to note the fact that there really is no science beyond this one guy's non peer reviewed article, and I'm glad to see that's the case, there isn't. Not that I worship science as some kind of deity that cannot be wrong, by the way, that's certainly not the case, but if we are in the world science defines, the rules there sort of have to be followed at some point. And science can be so hard and tedious, easier to just chat on forum threads.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: not science, not peer reviewed on 09/15/2012 20:12:04 MDT Print View

"science is sort of like a medieval guild system"

Egad. Don't let Roger Caffin read that.

Maybe he is out looking for a job as an alchemist.

--B.G.--

John S.
(jshann) - F
Re: not science, not peer reviewed on 09/15/2012 20:39:01 MDT Print View

Zell, Steven C. Epidemiology of wilderness-acquired diarrhea: implications for prevention and treatment. J Wild Med 1992;3:241-249.

"In the 1950s, Rendtdorff [18] studied the innoculum of Giardia lamblia cysts necessary to establish infection in federal prison volunteers. Known numbers of cysts were placed along with a small amount of saline into gelatin capsules ingested by subjects. Stool specimens from prisoners were examined for up to 165 days after exposure and infection defined as ability to identify Giardia lamblia cysts in the subject's stool, regardless of symptomatology. No person exposed to one cyst became infected, whereas 36.4% of 22 men receiving from 10-25 cysts established infection. All subjects receiving 100 cysts or more developed infection. Of note, no individual developed symptomatic giardiasis and there was a tendency for infections to disappear spontaneously over time [18]."

Rendtorff, R The experimental transmission of human intestinal protozoan parasites. Am J Hyg 1954; 59, 209-20.

John S.
(jshann) - F
Re: the science on 09/15/2012 20:47:48 MDT Print View

http://www.cdc.gov/parasites/giardia/epi.html

"However, swallowing as few as 10 cysts might cause someone to become ill[2,6]."

2. Yoder JS, Harral C, Beach MJ. Giardiasis surveillance - United States, 2006-2008. MMWR Surveill Summ. Jun 11 2010;59(6):15-25.
6. Rendtorff RC. The experimental transmission of human intestinal protozoan parasites. II. Giardia lamblia cysts given in capsules. Am J Hyg. Mar 1954;59(2):209-220.

John S.
(jshann) - F
Re: Re: the science on 09/15/2012 20:50:42 MDT Print View

http://www.cdc.gov/mmwr/preview/mmwrhtml/ss6105a2.htm?s_cid=ss6105a2_w

"The infectious dose is low; ingestion of 10 cysts has been reported to cause infection (12)."

12. Rendtorff RC. The experimental transmission of human intestinal protozoan parasites. II. Giardia lamblia cysts given in capsules. Am J Hygiene 1954;59:209–20.

Harald Hope
(hhope) - M

Locale: East Bay
old stuff on 09/15/2012 21:17:43 MDT Print View

My eyes aren't what they used to be, age catches us all, so I can't count how many cysts are in each liter I drink. Nor do I know what is upstream from me. Possibly others out there can, more power to them. So there's the 10 count, good, from a very old study. So that's one single fact now that's somewhat established. Unless it's been disproved in a more recent study, something that happens constantly, with newer methods and newer testing tools etc. So really what we are looking for is up to date data, but an old test is better than none. So did that liter I just downed have 0, 1 or 10 in it? See the absurdity? Hopefully yes. this is why I use a filter, and these discussions are what totally convinced me to always do that from now on, especially when I see how thin the actual research is.

Odd to find the CDC still keep noting 1 is all that is required on most of its documents, it's not like them to err on the side of care and caution, but figuring out what makes them decide x or y is a very challenging thing, I will happily admit, if they trust one doctor over others, and that doctor is corrupt, or lazy, or stuck in old habits, it leads to problems. Lots of ego, careerism, profiteering, corruption, etc, involved with these areas too, things change, and people who made their careers being experts in the old way, keep resisting change because the new way makes their studies less valuable.

However, I am left with the problem that I have no way of counting the cyst count per liter I drink today, here, from this water source I am at now, assuming I'm backpacking somewhere or other. And neither does anyone else. I'd be a fool to follow higher risk actions re pathogens when I can easily and with no effort follow lower risk actions, with exactly zero negative repercussions for me. Basically what we have is one cranky old physics professor, who has his pet peeve, and writes on it. That's not a new or rare thing in science, by the way, lots of professors do that, with the same lack of discipline.

But again, I truly do not care what other people do as long as they don't expect me to help them if they run into troubles based on their decisions. No common sense I can locate suggests that not filtering is a better idea than filtering, that simply makes no sense, so I will happily filter. But the added information is good, I wasn't sure about the cyst sizes, so that's clearly much less grounds for concern, and being aware of other backpackers as possible vectors is a good thing to know too, so that's a plus.

I was just checking to see if there was any actual new science on this question, there isn't apparently, so that's fine, the question is still relatively the same, except for worsening ecosystem degradation, which stresses things in all types of ways, most far too rapidly evolving to actually keep track of unless you specialize in the area. But one thing can be stated with absolute certainty: things are getting worse, and they are getting worse quickly. Which parts of our ecosystem react in which way, that is something being studied with more energy now than in the past, for obvious reasons. So anyway, there's no debate I can find here, just some slightly improved understanding of the question. As I thought.

Still unanswered, my original question that started my readings: how long does a giardia cyst live in the air, out of water or outside of fecal matter, ie, a drop of water dries? However, if the 10 count is accurate, I'd say that question is also somewhat mooted, would be more relevant if 1 is sufficient. It's odd how hard it is to find answers to even simple questions like that, I think that reflects the state of the research fairly well is my guess.

And, other questions, is the count of cysts cumulative, ie, over 2 days and 4 liters, do 10 total count? Or does it have to be 10 per ingestion? Has anyone ever tested this? I seriously doubt it. There's a fair degree of wishful thinking going on here about what is actually being said I suspect. So much not known here, zero grounds to make any statements about safety in my opinion, and I suspect that is what makes the CDC err, as they should, on the side of caution. I'm leaving this one alone, categorizing it as wishful thinking, best argument for filtering I've seen yet, thanks.

Edited by hhope on 09/15/2012 21:36:43 MDT.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: old stuff on 09/15/2012 21:41:18 MDT Print View

"the 10 count"

I think that is because different humans have immune systems of different powers. One person might be fragile, and one cyst might be able to set up housekeeping in the gut and make a living at it. One person might be tough and have an excellent set of biochemical acids, so ten cysts can be wiped out before they make a go of it. Maybe one person had a strong dose of coffee and that helped to devitalize the critters. We will likely never know.

Where I was this week is where a close friend contracted Giardia 25 years ago (swimming in the lake). So, I filter every drop for consumption.

--B.G.--

William Segraves
(sbill9000) - F - M
infection rate per cyst on 09/16/2012 05:27:26 MDT Print View

This has been an interesting thread, but as others have observed, there are some real gaps in the science.

Harald asks a key question, perhaps *the* key question: "is the count of cysts cumulative, ie, over 2 days and 4 liters, do 10 total count? Or does it have to be 10 per ingestion?"

I might place the emphasis slightly differently - does the probability of infection from a given exposure increasingly linearly with the number of cysts ingested? (The alternatives being that there is a key threshold or simply a greater than linear increase in probability due to "cooperativity." And if the answer's that it's non-linear, then we have to move on to Harald's question about the timing.)

Everything I've seen (big caveat - I have not looked exhaustively) is consistent with a linear response and a human infection rate of ~ 1-2%/viable cyst (n.b., viable is very important here, if/when we start parsing data for consistency with this). In the most commonly cited human study, one cyst didn't infect anyone because they didn't test enough people to overcome the odds. Unfortunately, everything I've seen is also consistent with the other two possibilities I've posited above!

Given that concentrations of cysts in most contaminated wilderness water sources is low, this is what I would most want to know. It seems pretty clear that my chances of getting infected from a single half liter drink of reasonably well-chosen wilderness water are low. Hypothetically, let's say that I'm backpacking in an area where I can consistently limit my exposure to the order of 1 cyst/20 liters by choosing my water well. If there's a threshold or a significant non-linearity to infection rate/cyst (and cumulative effects are relevant only on the order of a day), I can expect to drink happily for a long time without becoming infected. But if it's linear or approximately linear, my luck will run out, and on a timescale that's relevant.

If there's a good study that addresses this question, please, someone point it out! And if not, for now, we sift through the clues that may exist within other available information.

Best,

Bill S.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Giardia Cyst Counts, etc on 09/16/2012 14:24:21 MDT Print View

The cited Rendtorff study seems to be the basis for most or all of the infectious dose numbers. Most people got giardiasis at the 10+ cyst level. Five men got one cyst one time and didn't get giardiasis. No one was tested for 2,3,4,5,6,7,8, or 9 cysts. Obviously the 10+ infectious dose number isn't valid statistically yet it is a vital part of the argument against waterborne giardiasis for backpackers.

Someone said I disagree with your conclusion that the cited references establish "...there is more scientific evidence to support the spread of Giardiasis through water than there is through hygiene. I didn't mean which cause is the more common. I'm not sure what the ratio is and I don't think anyone does. What I mean is there are several studies saying something along this line:
"drinking untreated backcountry water is an important cause of endemic giardiasis infection" with no studies that I'm aware of making this sort of claim:
"poor hygiene in the backcountry is an important cause of endemic giardiasis infection." Welch and Rockwell have made statements approaching the latter, but only after basing those statements on lack of evidence for waterborne giardiasis.

I believe that most of these studies are going about it the wrong way anyway. Retrospective surveys seem wisest to me, like the Colorado study where they surveyed 256 giardiasis cases and determined that the infection rate was triple for those not treating. That is significant. It didn't matter how many cysts there were or how viable the cysts were or when and where the tests were done or even what the infectious dose was. At the time we are drinking from backcountry sources it is essentially untested water so viable cyst counts aren't available and the big picture stats are more valuable for risk analysis.

Harald said So my quest for the science of it showed almost no variation in the data or information, and all of it said the same thing. Where exactly is the alleged 'science' going on that is disproving categorically the cdc and other government findings, making for an actual scientific disagreement? It's just one guy, right, who publishes some stuff online, correct? Typical internet stuff, right? Or is there real science going on somewhere?

Much of the "science" comes from the paper I am currently trying to debunk. It is the cornerstone of the infamous Giardia Myth-Buster paper which I find appalling, especially in his heavy use of cherry-picked anecdotal evidence. He posted that article all over the internet to the delight of people who had just learned that science had proven that untreated drinking water is safe to drink.

In a forum post about what he considers excessive paranoia about giardia he actually said nearly all warnings state that all water is polluted with Giardia. He also said Someone wrote about other threats in the water: "...Giardia is not the only thing to worry about in the back country. with the increased human waste problem in the high peaks, bugs like e-coli, VRE, and Hepatitis are real possibilities too."

These are not real possibilities -- no studies have shown these threats to be of concern to backpackers who do not treat their water.
That is some highly irresponsible "science."

Of course Rockwell did a lot of research and cited many legitimate scientific sources but his conclusion to "drink freely" was based largely on the Welch paper currently being discussed.

Edited by Colter on 09/16/2012 14:32:14 MDT.

Bill Law
(williamlaw) - M

Locale: SF Bay Area
Re: not science, not peer reviewed on 09/16/2012 16:24:38 MDT Print View

That's just a guy, talking about one area, that he likes to hike in. It's not science, even though he's a scientist.

Can be good to start a conversation though, I'd certainly not follow anything he says beyond that.


Good point. I stopped reading your (lengthy!) post at this point :-).

That paper maybe hasn't been "peer reviewed" in the sense you imply, but in terms of being read, discussed, and contemplated on by fellow travelers in the Sierra, it most certainly has. And in some ways, that's worth a lot more than some academic critique.

"Put your money where your mouth is," if you will.

Go read the "peer reviewed" studies he cites if you don't believe him.

The OP (so far as I know) hasn't had his blog post peer reviewed. Shoot; he's asking us here to review it for cripes sake.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Peer review on 09/16/2012 17:38:15 MDT Print View

That paper maybe hasn't been "peer reviewed" in the sense you imply, but in terms of being read, discussed, and contemplated on by fellow travelers in the Sierra, it most certainly has. And in some ways, that's worth a lot more than some academic critique.

"Put your money where your mouth is," if you will.

Go read the "peer reviewed" studies he cites if you don't believe him.


The conclusions of the Rockwell paper seem so plausible largely because of all the peer reviewed papers he cites. It's easy to conclude that with all those citations that they must agree with his "drink freely" philosophy. But if you read them, almost none of them do, except for those written by Welch or other paper's Rockwell has written. If cited sources take a stand on the issue, they almost always say waterborne giardiasis in the backcountry is a concern. Anyone can read through piles of peer reviewed papers and pick and choose certain data to support what might be invalid conclusions.

You are right that the Rockwell paper is likely the most read and discussed paper on the topic. That doesn't make it accurate of course. Apparently many readers don't buy his conclusions because most people in the Sierras still treat their water.

I devote most of this post to debunking the Rockwell paper. The orignal post here was directed at a Welch paper which covers less ground, making it simpler to refute and discuss.

Not surprisingly my blog posts have not been peer reviewed in the conventional sense. That's why I came here to be reviewed by my peers! I want to identify the flaws. There are educated people here with a critical eye who will not hesitate to point out logical fallacies, I'm sure.

This continues to be one of the best, most rational discussions I've ever seen on the topic. Keep it coming!

Edited by Colter on 09/16/2012 17:43:40 MDT.

Bill Law
(williamlaw) - M

Locale: SF Bay Area
Re: old stuff on 09/16/2012 17:42:18 MDT Print View

I'd be a fool to follow higher risk actions re pathogens when I can easily and with no effort follow lower risk actions, with exactly zero negative repercussions for me.

A negative repercussion for me is to be unable to walk along a trail in the wilderness and simply dip my cup into a free-flowing stream and enjoy a refreshing, cold, drink. I'd be a fool to give that up to protect against a risk that does not appear to exist.

Basically what we have is one cranky old physics professor, who has his pet peeve, and writes on it.

Your arguments might carry more weight if they omitted such ad hominem attacks. Attacks, BTW, which blatantly ignore what the man has contributed by sharing his experience and expertise, not to mention his life-long public service to the community of like-minded Sierra travellers.

It makes you come across as a bit, well, "cranky."

Katy Anderson
(KatyAnderson) - F
math on 09/16/2012 17:49:47 MDT Print View

I have a different reading of the math.

Bruce said:
"Retrospective surveys seem wisest to me, like the Colorado study where they surveyed 256 giardiasis cases and determined that the infection rate was triple for those not treating."

This is how they word it in the summary for the study:
"A statewide telephone survey of 256 cases and matched controls identified: 1) and increased incidence of giardiasis in persons between the ages of 16 and 45, p less than .001, with males and females equally affected; and 2) a higher proportion of cases than controls who visited Colorado mountains (69% vs. 47%), camped out overnight (38% vs. 18%), and drank untreated mountain water (50% vs. 17%), p less than .001."

I read that as: the giardia infected group was three times more likely than the control group to drink untreated mountain water, twice as likely to camp out overnight and somewhat more likely to visit the mountains.

What you did with these numbers was to say: if three times as many people in the infected group drank untreated water then it follows that untreated water is three times as infectious as treated water. I think that is an incorrect conclusion.

Bill Law
(williamlaw) - M

Locale: SF Bay Area
Re: Peer review on 09/16/2012 18:06:43 MDT Print View

What, precisely, might you mean by the phrase "is a concern?"

One can find studies that show incredibly low numbers of giardia cysts being found in Sierra water sources. Way lower than municipal water supplies, apparently (I don't know if the cited levels are at the source, or coming out of the tap).

One offhand statement in a study cited above is this: "Of note, no individual developed symptomatic giardiasis and there was a tendency for infections to disappear spontaneously over time [18]."

Headline: Studies show that 100% of giardia infectees exhibit no symptoms, and it cures itself!

So what's the risk we're talking about? Getting a disease that nobody will notice, and which goes away without doing anything?

I need *more* diseases like that one, not less.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Control Groups on 09/16/2012 18:23:22 MDT Print View

Katy said:

What you did with these numbers was to say: if three times as many people in the infected group drank untreated water then it follows that untreated water is three times as infectious as treated water. I think that is an incorrect conclusion.

Hmmm. That's something to ponder. "(Matched control) In statistics, matching is comparing groups in which each subject is matched by a comparable subject (called matched or paired control) in terms of age and all other measurable parameters, optimally being equal in every aspect except the exposure of interest."

My reading, accurate or not, is that the matched control would be as equal as possible in every way except for the treatment of water.

If I'm wrong I wonder how the control group was chosen? Would they possibly have people in the control group that had been drinking untreated water?

Katy Anderson
(KatyAnderson) - F
Re: Control groups on 09/16/2012 18:42:02 MDT Print View

The way I read it is that the control group are uninfected by giardia.

Buck Nelson
(Colter) - MLife

Locale: Alaska
re: re: Peer review on 09/16/2012 19:58:21 MDT Print View

Bill, by "waterborne giardiasis in the backcountry is a concern" I mean that giardia is often present and drinking the water might result in an infection.

No offense intended, but you really need to read through the thread so we don't have to keep rehashing the same stuff. The "city water is dirtier than Sierra water" has been debunked.

One offhand statement in a study cited above is this: "Of note, no individual developed symptomatic giardiasis and there was a tendency for infections to disappear spontaneously over time [18]."

Headline: Studies show that 100% of giardia infectees exhibit no symptoms, and it cures itself!

So what's the risk we're talking about? Getting a disease that nobody will notice, and which goes away without doing anything?


This is a classic example of the type of disinformation that's out there.

In the large Colorado study they found this: The majority of infected residents who were surveyed had experienced an episode of chronic watery diarrhea (median duration 3.8 weeks) with bloating, flatulence, and weight loss (averaging 5.1 kg)

So sick for an average of 3.8 weeks and losing over 11 pounds. Not exactly 100% of giardia infectees exhibit no symptoms, and it cures itself!

Harald Hope
(hhope) - M

Locale: East Bay
more stuff on 09/16/2012 21:08:57 MDT Print View

Here's a good one I found by a guy who was stupid enough to fall for that Rockwell paper when hiking the PCT:
http://bucktrack.blogspot.com/2011/03/waterborne-giardia-for-backpackers-no.html

Years ago I twice contracted Giardiasis, in consecutive years. Since the second time I have been very careful about treating water, and had no trouble for many years. However, before I left on my five month thru-hike of the Pacific Crest Trail last year, I read this article. Giardia lamblia and Giardiasis With Particular Attention to the Sierra Nevada. It made a very convincing case that the odds of getting Giardia from backcountry drinking water was so low it didn't pay to worry about, at least in the High Sierras, as long as some attempt was made to select water sources. Instead, a focus on hygiene was stressed. So on the PCT I usually didn't treat my water. But I was the most careful I've ever been with hygiene in the outdoors. Unfortunately I got so sick in the Sierras that I was curled up on a mountainside, and it took me most of a day to make it the four miles (only four, luckily) to the nearest road. I partially recovered, after a full day of rest, then a week later became very sick again. Luckily I was at Mammoth Lakes. My physician diagnosed Giardia. He told me he treats many backpacker Giardia cases and doesn't report it. He laughed when I told him about the article I read. Other hikers have told me their doctors told them the same. A cursory scanning of Pacific Crest Trail sources shows about 12 thru-hikers a year (out of around 300) report getting giardiasis. And despite statements to the contrary, most are diagnosed by lab tests and/or physicians. With 2/3 of people being asymptomatic, the true number is likely much higher.


This guy lists some recent studies as well that show the Rockwell thing to be nothing more than wishful thinking and pseudoscience.

I read some other more scientific stuff, the only real takeaway there is things like it takes from 1 day to 10 days to come down with it. the amount of totally wrong information in this community on this topic is somewhat staggering, maybe think about not citing articles that cherry pick their data to confirm their premise?

Anyway, as I noted, I'm now totally sold.

I like this guy's blog posting because he's no longer engaging in wishful thinking, and probably no longer thinks that saving 3oz of pack weight is a very good idea, I could have told him that if he'd asked, of course.

So people reading this thread, be warned, you're looking at a myth that people are trying to spread, not science, keep filtering, boiling, treating whatever, and ignore people who make claims about it not being necessary.

http://download.journals.elsevierhealth.com/pdfs/journals/0953-9859/PIIS0953985993711729.pdf
http://www.ncbi.nlm.nih.gov/pubmed/937629

I mean, really, let's move on to debating silnylon vs cuben, bpl is good at that, clearly when wishful thinking gets involved, something goes wrong. I had my suspicions when I first came across people in the backpacking scene trying to spread this myth, it had that smell of pseudoscience about it, ie, primary source not science, relies on anecdotal evidence and cherry picking of data, all the telltale warning signs.

It is good however to now and then re-examine such things, but the notion that backcountry is getting healthier is almost too far fetched to take seriously now, best to adjust to reality and move on to trying to drop pack weight without skipping water treatment.

Another telltale is just how easy it is to find stuff that shows the myth as myth, and how hard it is to find real science that supports it.

But bpl is a good place to hash over such things, but when it comes to medical stuff, I'm looking elsewhere for good advice, just like that guy I quote above wishes he did.

His article is good, he goes through almost everything people in this thread are citing, including that single study on number of cysts required. I'd stop spreading this garbage if I were you guys who keep promoting that junk science of Rockwell's, it's bad for people's health and it really isn't cool. I like the part about his doctors laughing when they saw Rockwell's paper, that kind of says it all, don't you think? I'd be embarrassed personally to spread this nonsense, and will make a point of noting the fact it's nonsense in future threads on this topic to help save some uncritical souls who might believe the fake non research so they can break that SUL barrier or whatever other reason people come up with for having to cut those 3 ounces.

But we do learn, and one thing I learned is that in fact, some people don't get this, only about 30% or so do. That means, for those counting, that a bit over 10% of PCT thruhikers get it every year, or maybe even more, though only 1/3 of them get sick from the stuff. That also explains the people who note they've never gotten sick, seems like there's variations in how sensitive one's body is to it, or something, those accounts can well be true, but have no meaning for your body.

Edited by hhope on 09/16/2012 21:37:30 MDT.

Katy Anderson
(KatyAnderson) - F
more fun with numbers on 09/16/2012 21:30:28 MDT Print View

Looking further at the abstract for the 1977 study in Colorado, I see some interesting numbers.

"A one-year retrospective laboratory survey in Colorado revealed that 691 (3%) of 22,743 stool examinations for ova and parasites were positive for Giardia lamblia, a higher percentage than that reported from surveys outside of Colorado."

That means that out of 100 people who had persistent stomach upset, went to the doctor, and convinced the doctor to order an ova and parasite test, only 3 of them were found to have giardia.

"a higher proportion of cases than controls who visited Colorado mountains (69% vs. 47%), camped out overnight (38% vs. 18%), and drank untreated mountain water (50% vs. 17%)"
So if 17% of the Colorado population of about 4 million in 1977 drank untreated water that would be 680,000 people. Out of these 691 tested positive for giardia, that is a 0.1% lab identified infection rate. This is assuming that all giardia cases in Colorado were caused by drinking untreated water, which of course is an overestimate.

So if you drank untreated water in Colorado in 1977 you had less than 1 in a 1000 chance of catching giardia so bad that you went to the doctor and got it lab tested and confirmed.

I'm a nerd but not a statistician, so if I am reading this wrong let me know.

Edited by KatyAnderson on 09/16/2012 21:36:36 MDT.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Looking into the giardiasis numbers on 09/17/2012 04:28:34 MDT Print View

Katy said: A one-year retrospective laboratory survey in Colorado revealed that 691 (3%) of 22,743 stool examinations for ova and parasites were positive for Giardia lamblia, a higher percentage than that reported from surveys outside of Colorado."

That means that out of 100 people who had persistent stomach upset, went to the doctor, and convinced the doctor to order an ova and parasite test, only 3 of them were found to have giardia.


I don't think that can be true. 3% is, as they noted, "a higher percentage than that reported from surveys outside of Colorado" [who have giardia] so it must be cross section of the public in general. I believe something over 2% of people in the U.S. have giardiasis. Most backpackers I know who are tested for giardia come up positive.

Oh, coincidentally, I was the guy Harald quoted above who was stupid enough to believe the "giardia myth" papers. That is what triggered my research.

Edited by Colter on 09/17/2012 05:04:27 MDT.

William Segraves
(sbill9000) - F - M
Re: re: re: Peer review on 09/17/2012 04:40:21 MDT Print View

> The "city water is dirtier than Sierra water" has been debunked.

Can you direct me to where this has been "debunked"? It's one of the three key pieces of evidence, and perhaps the most germane.

Thanks.

Bill S.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: re: re: Peer review on 09/17/2012 05:01:54 MDT Print View

To quote what I've written earlier: A major theme in the Rockwell paper is that Sierra water on average is purer than San Francisco and LA water. Except for two big factors: these cities filter and/or treat their water supplies, so they are undoubtedly much safer than untreated Sierra water. And hikers don't drink an "average" canteen of water. Their water bottle might contain no Giardia cysts, or they might get enough cysts to send them to the hospital.

http://bucktrack.blogspot.com/2011/03/waterborne-giardia-for-backpackers-no.html

I would also add that the giardia numbers used for the Sierras are decades old and undependable.

William Segraves
(sbill9000) - F - M
Sierra vs SF or LA water on 09/17/2012 06:29:20 MDT Print View

Bruce,

In my opinion, if you want to refute the validity of the comparisons among Sierra and California city water supplies, you need to dig deeper into the data and show exactly where and how they're flawed. I have only looked at a few of the reports in detail, but if I have understood and recall them correctly, the Hetch Hetchy water feeding the Bay area was considered clean enough not to require filtration. If that's the case, then the count comparison per se may well be valid.

What you may want to look into is whether there's evidence that would bear upon the viability of those cysts. If I've understood correctly, the water does get chlorinated, and while the relevant chlorine concentrations would be inadequate for purifying a more highly contaminated source in the field, they may be enough - over an extended period of exposure - to knock the viable cyst count down significantly (i.e., to a level well below that of contaminated Sierra sources). Just to be clear, I'm speculating as to what you might find, but I think that's the place to be looking for clues.

The other place, as I've intimated before, is the original data on the number of cysts required for infection. Some oft-cited sources have taken the data to say that infection cannot occur below a 10 cyst exposure (or that the probably is dramatically lower at lower exposures), a clear mis-interpretation of the findings. The implications for the potential infectivity of water with low level contamination are huge. Finding ten in a given liter of water at typical measured Sierra levels is enormously improbable. Finding one is going to happen a lot more often.

And you are right, of course, that it's inappropriate to draw conclusions that assume that cysts are randomly distributed in Sierra water. This profoundly alters the odds that have been calculated based on measured concentrations (interestingly, unless one cyst is a tenth as likely to infect you as ten cysts).

Bill S.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Good points Bill on 09/17/2012 07:48:28 MDT Print View

At some point enough is enough on digging too deep in a blog post. The typical person is unlikely to read all the way through a long post with citations as it is. If it were a paper for peer review, you'd probably be right.

I know Hetch Hetchy water is run through water treatment plants and is treated with Chloramine. I found this quote: "Giardia cysts can be inactivated by free chlorine at 0 to 25 degrees Celsius, or with carbon dioxide, ozone, or chloramine." (What's In the Water? Climate Change, Waterborne Pathogens, and the Safety of the Rural Alaskan Water Supply) The Rockwell paper failed to mention treatment plants at all. One skeptic, a friend of Rockwell, pointed out it was because at the time they were using chlorine and chlorine is ineffective. If that's the truth, Rockwell was wrong on that as well:Due to a misstatement in the early literature, Giardia cysts have been considered for many years to be extremely resistant to disinfection...Several studies have shown that as little as 2 mg of chlorine per liter can kill greater than 99.8% of the Giardia cysts

http://www.tandfonline.com/doi/abs/10.1080/10643388809388341

I think we can agree that the whole city/Sierra concentrion argument is invalid from the get-go anyway because high concentrations of viable giardia cysts are dramatically more likely in the Sierras compared to a city hundreds of miles away, especially after it's been run through a water treatment plant.

Katy Anderson
(KatyAnderson) - F
math and science on 09/17/2012 09:36:03 MDT Print View

Sorry to drill down on this, but if we are to discuss science we have to look carefully at the numbers in these studies and try to understand what they mean.

Katy said: (the quote is from the 1977 study abstract)
"A one-year retrospective laboratory survey in Colorado revealed that 691 (3%) of 22,743 stool examinations for ova and parasites were positive for Giardia lamblia, a higher percentage than that reported from surveys outside of Colorado."

That means that out of 100 people who had persistent stomach upset, went to the doctor, and convinced the doctor to order an ova and parasite test, only 3 of them were found to have giardia.

Bruce said:
I don't think that can be true.

Katy says:
True or not, what this study found was that 3% of the stool exams were positive.

Bruce said:
3% is, as they noted, "a higher percentage than that reported from surveys outside of Colorado" [who have giardia] so it must be cross section of the public in general.

Katy says:
If it was a cross section of the public that would mean that 22,743 healthy people in Colorado had a ova and parasite stool test done for research purposes in 1977. Seems unlikely.
Instead I believe "a retrospective laboratory survey" is a study where they do a statistical analysis of existing lab results.
So these ova and parasite stool exams were done on patients rather than healthy research subjects. Yet only 3% showed up positive for giardia.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Colorado Survey on 09/17/2012 10:50:38 MDT Print View

Hi Katy,

It's good that you don't just accept things as they appear to be on the surface.

One thing I've learned early on in this research is to step back and ask "here's what the numbers seem to show. Does this make sense?"

I don't doubt the 3% number. I doubt highly that it was 3% of people that had symptoms that physicians believed warranted a giardiasis test, if that is what you are saying. The overall incidence of infection in the United States is estimated at 2% of the population (FDA.) Colorado has a reputation for a higher than average infection rate. I think the ability of a physician to diagnose giardiasis is much better than random chance.

Perhaps the tests were from people with unidentifiable stomach ailments. I don't know. Too bad there isn't free public access to the full report.

Thanks for the skepticism!

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: math and science on 09/17/2012 11:33:23 MDT Print View

Does it matter if people are infected with no symptoms? They might pass it on to other people or animals, but we should already treat fec es as though it's infected with whatever. One theory says we're too hygenic - if we are exposed to some bugs we're less likely to have auto-immune diseases.

Another question is, does treating water prevent you from getting infected? maybe with or without symptoms?

Like, people say that they got Giardiosis from swimming - but that's irrelevant to the question of treating water. Or people have said they got Giardiosis even though they treated their water - maybe that would indicate that it's hopeless so don't worry about it or you have to do it more carefully.

A good study would be to select 100 people at a trailhead, randomly either select no water treatment or either of several treatments, maybe give them good instruction how to properly treat, test them before and after a backpack trip. You'de still have a bias because only some people would agree to it.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: math and science on 09/17/2012 11:41:53 MDT Print View

"A good study would be to select 100 people at a trailhead"

Most studies get better results if they are blind studies. In other words, the testees can't know exactly what method they are using. In the case of water treatment, I don't see how you could do that very easily.

Now, if you had three different chemicals that you wanted to compare, you could give one chemical to members of different groups, and they would not know exactly which one they got. Then you would have a control group that got nothing or a placebo, and you might have another control group that was using something completely different like a filter.

I don't want to be in a group that gets nothing.

--B.G.--

Katy Anderson
(KatyAnderson) - F
Colorado study full report on 09/17/2012 11:50:45 MDT Print View

Bruce said:
Too bad there isn't free public access to the full report.

Katy says:
Agreed, without the full report of the Colorado study it is hard to draw any conclusions from these numbers.
Who exactly got the o&p stool test? Healthy study subjects or sick patients?
How was the control group selected?
Your assumption was that they divided them into two groups dependent on whether or not they treated their water and then reported giardia infection numbers for each group.
My assumption was that they compared the giardia infected subjects to a healthy control group, and reported behavior numbers (drank untreated, camped overnight, visited Colorado mountains) for each group.
Depending on which assumption is correct yields a very different reading of this study.

Bruce said:
Thanks for the skepticism!

Katy says:
Thanks for bringing this topic up for discussion in a way that tries to analyze the underlying science rather than rehash everybodies opinions.
And especially thanks for putting up with me taking apart every number and data point in order to come to the bottom of the science.

Buck Nelson
(Colter) - MLife

Locale: Alaska
More numbers on 09/18/2012 04:21:05 MDT Print View

Katy said: So if 17% of the Colorado population of about 4 million in 1977 drank untreated water that would be 680,000 people. Out of these 691 tested positive for giardia, that is a 0.1% lab identified infection rate. This is assuming that all giardia cases in Colorado were caused by drinking untreated water, which of course is an overestimate.

So if you drank untreated water in Colorado in 1977 you had less than 1 in a 1000 chance of catching giardia so bad that you went to the doctor and got it lab tested and confirmed.


I think we need to read the full report! These are all good arguments making me think, for sure.

Assuming your calculations are true, another way to look at those above numbers would be that over an 80 year lifetime you'd have an 8% chance of catching giardiasis so bad you'd be sick for a month. Several times the risk for a person who spends a lot of time in backcountry. If a typical Coloradan drinks untreated water one day a year, which seems high, actually, the typical thru-hiker might drink untreated water 100+ days a year if they aren't treating. All things being equal, they might go from 1 out of a thousand to 1 out of 10 chances of getting serious giardiasis that year. All fuzzy numbers, of course.

Like you say, though, a significant proportion of cases aren't caused by drinking bad water at all. On the other hand, many bad cases go undiagnosed and run their course. Many cases are treated empirically and never lab tested. Most cases are asymptomatic. People with giardiasis often come up with a negative test. And as I found out in my research, nearly 99% of cases go unreported. I'm not sure how that would affect the Colorado study. I do know the author's concluded These results indicated that G. lamblia is endemic in Colorado and that drinking untreated mountain water is an important cause of endemic infection.

Edited by Colter on 09/18/2012 04:23:08 MDT.

William Segraves
(sbill9000) - F - M
Re: More numbers on 09/18/2012 06:57:36 MDT Print View

The study was based on 1973 population of 2.1 million. From the study, half of identified infections were in people who didn't report drinking untreated water. Those two factors offset - as a thumbnail calculation, the water drinkers had about a 1/1000 chance of winding up with diagnosed giardiasis in a given year. Backpackers' risk will be higher, since they almost certainly drink more often than the average person, but the one day/year estimate above for the average untreated water drinker is too low. Assuming accurate reporting, the 17% all drank at least once - in the absence of data, what the distribution and its average would be is anyone's guess, but my WAG would be closer to 10 than 1.

FWIW, you can push the numbers a bit farther, if you wish, to get a rough estimate that untreated water-drinkers were about 5 x more likely to contract diagnosed giardia than non-drinkers.

The definitions of cases and controls were as expected per correspondence above:

"A case was defined as any person having a positive stool specimen for G. lamblia during the study year. A questionnaire was administered by telephone to each case and to controls matched by age, race, sex, and place of residence."

Best,

Bill S.

Katy Anderson
(KatyAnderson) - F
numbers on 09/18/2012 09:59:36 MDT Print View

Bill said:
FWIW, you can push the numbers a bit farther, if you wish, to get a rough estimate that untreated water-drinkers were about 5 x more likely to contract diagnosed giardia than non-drinkers.

Katy says:
Interesting. Can you walk me through that calculation?

William Segraves
(sbill9000) - F - M
Re: numbers on 09/18/2012 19:01:09 MDT Print View

Katy says: Interesting. Can you walk me through that calculation?

Here's one of the ways to get there: about 1/6 of the population drinks untreated water, 5/6 does not. There are 1/5 as many drinkers as non-drinkers, but they account for equal #s of cases (the 50-50 split among affected individuals). For that to happen, drinkers have to be ~ 5 x as likely to be affected. Make sense?

Best,

Bill S.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Cases, Controls, what it means on 09/18/2012 19:25:25 MDT Print View

Bill said: "A case was defined as any person having a positive stool specimen for G. lamblia during the study year. A questionnaire was administered by telephone to each case and to controls matched by age, race, sex, and place of residence."

Good stuff Bill, where did you get the above information?

It looks like you were right about the controls, Katy. And likely about the original pool of people having already been tested before the study.

Bill said: "Here's one of the ways to get there: about 1/6 of the population drinks untreated water, 5/6 does not. There are 1/5 as many drinkers as non-drinkers, but they account for equal #s of cases (the 50-50 split among affected individuals). For that to happen, drinkers have to be ~ 5 x as likely to be affected."

Very interesting. I'm pretty sure I would never have looked at it that way!

I would like to note that so far we have escaped Godwin's Law. http://en.wikipedia.org/wiki/Godwin's_law

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Cases, Controls, what it means on 09/18/2012 20:10:36 MDT Print View

Does just mentioning "Goodwin's Law" mean that we have now made a Nazi reference so the discussion is ended?

and since you brought it up, you lost?

or does my mentioning Nazis mean that it's ended and I've lost?

Katy Anderson
(KatyAnderson) - F
5 x on 09/18/2012 20:13:56 MDT Print View

Thanks Bill, your explanation makes perfect sense.

Bruce now you can go back and edit your blog post:
"Welch makes an even more egregious "mistake" in Giardiasis from Wilderness Water. Citing Giardiasis in Colorado: an epidemiologic study he says Responses indicated that 38% of cases vs 18% of controls had camped overnight in backcountry areas. He ignores the very next line in the abstract to that paper which says and drank untreated mountain water (50% vs. 17%.) There it is, in black and white. The infection rate was TRIPLE for drinking untreated mountain water in this large group. I think it's a great example of confirmation bias and is bad science, at best."

The correct reading of this data is that there is FIVE TIMES the infection rate.
So if you drank untreated you had 1 in 1000 rate of lab diagnosed Giardia infection in any given year, whereas if you treated your water you would have 1 in 5000 rate of lab diagnosed Giardia infection in any given year.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: 5 x on 09/18/2012 20:23:48 MDT Print View

But if you had only a 1 in 1000 chance of being infected in one year, it's hardly worth thinking about.

And if you got unlucky, it's obnoxious but surviveable. And I'll normally be back home.

I keep going back and forth whether I'll bother treating water.

Buck Nelson
(Colter) - MLife

Locale: Alaska
So, Hygiene vs Waterborne Giardiasis? on 09/19/2012 04:06:06 MDT Print View

A recurring theme for Welch and Rockwell is that it's hygiene, not the water, that's causing giardiasis for backpackers. What can be concluded from this study?

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: 5 x on 09/19/2012 04:34:34 MDT Print View

"But if you had only a 1 in 1000 chance of being infected in one year, it's hardly worth thinking about."

The problem there is that the disease presents itself with a multitude of symptoms of varying intensity.

Example 1. (about 1988) A backpacker friend of mine swam in the lake, then about ten days later there was a slow onset of standard symptoms of mild intensity. After a couple of days, the friend was at the doctor's office. After a couple of more days, the lab test confirmed it. A rather standard dose of medicine was prescribed, and the problem slowly went away.

Example 2. (1983) A Nepal trekker may have been infected by water vessels that were not properly washed. She got explosive diarrhea about eight days later. We are talking about ten or more trips to the bushes in one day. That same afternoon, a microscopic analysis was done, and it was overwhelmingly obvious that cysts were present by the billions. Good grief! She was given a four-day dose of Flagyl within 24 hours, and the problem started to clear. She was weak as a kitten for the next four or five days and then was not back to normal by the end of the trek another week after that. Incidentally, half of the other trekkers developed milder forms of it as well, so they knew where to find the doctor with the drugs.

Two extremely different examples. The first one was more tolerable. The second was not.

--B.G.--

Buck Nelson
(Colter) - MLife

Locale: Alaska
Careful with the numbers though on 09/19/2012 04:54:12 MDT Print View

Jerry said "But if you had only a 1 in 1000 chance of being infected in one year, it's hardly worth thinking about."

When I read the Welch and Rockwell papers, I was getting ready for the PCT. My take away message was that the odds of waterborne transmission were near zero for backpackers. I got giardiasis.

While I think a solid finding from this study is waterborne transmission is a reality, it would be risky to depend on the numbers to calculate our personal odds. For example, some people rarely drink untreated water and are highly resistant to giardia so their risk of getting sick would be dramatically lower. I often drink backcountry water for months every year and am susceptible to giardiasis. My odds are likely orders of magnitude higher than normal. This study is decades old and for only one geographic area.

And, as I mentioned above, physicians often empirically treat (no lab tests,) fail to report (in Modoc County CA I found that no cases were reported over 3 years despite the doctor saying they treat several cases per week) and many people never go in for treatment at all, despite being sick.

An example of how this kind of under-reporting can mislead an odds calculation would be that in the United States there are about 2,000,000 plus people with Giardiasis. Of these cases, about 20,000 are reported per year. With 300,000,000 people, the odds of getting giardiasis are 1/150 in reality. The odds based on reported cases are 1/15,000. Big, big difference. And if the odds of getting giardiasis (very often asymptomatic) are 1/150 to begin with, the odds of getting it in a year if you drink untreated water too would have to be higher yet.

Another consideration is giardia is only one of the baddies that might be in backcountry drinking water.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: 5 x on 09/19/2012 08:55:51 MDT Print View

Not to be argumentative Bob, just trying to figure out how much to worry about treating my water

Example 1 lesson - don't drink lake water when swimming

Example 2 lesson - when in Nepal don't depend on a third party to treat your water

Bruce - I agree, if you've gotten Giardiosis before then it makes sense to religiously treat water

I treat my water about half the time. I don't bother if the water is coming out of a spring, or from a snow-field I can see (although there could be a dead critter underneath), or if up-stream is wilderness and there's good stream flow to dilute anything and it looks clear. I haven't (knock on wood) gotten sick and have done this at least 100 days.

I have this stuborness about not doing things that aren't necesary, but the Sawyer Squeeze is so convenient and lightweight - if it only didn't have this weakness about freezing because I go when it's below freezing a lot.

William Segraves
(sbill9000) - F - M
water quality comparisons on 09/19/2012 16:27:50 MDT Print View

Catching up on an older part of the thread, and not disagreeing, just adding my $.02.

IMO, the water quality comparisons are relevant, and should not be dismissed without a careful analysis of their strengths and weaknesses. That they may predate the current water treatment methods does not diminish their potential value - if the water was OK for 5 million people in 2000 and it was more highly contaminated than Sierra water, then that tells us something important.

But was it? The trail of information is sketchy, as far as I can tell, but it appears that the cyst concentrations in LA and SF Bay area water were in the same general range as tested Sierra sources. What isn't at all clear is what proportion of those cysts may have been viable. As far as I can tell, those water supplies were being chlorinated, and various authors may have extrapolated from older studies that appear to have exaggerated giardial cyst chlorine resistance to conclude that chlorination was not substantially reducing potential giardia infection. My reading of a key Jarroll et al 1981 paper, "Effect of Chlorine on Giardia lamblia Cyst Viability," suggests the contrary: even at 5 degrees C and pH 7, 1 mg/L is sufficient to achieve 98% killing in an hour.

Best,

Bill S.

William Segraves
(sbill9000) - F - M
Re: Re: 5 x on 09/19/2012 17:41:44 MDT Print View

"But if you had only a 1 in 1000 chance of being infected in one year, it's hardly worth thinking about."

I agree, but while 1/1000 is the approximate chance of winding up in the CO case group, it seems clear that this would have been a substantial underestimate of the likelihood of contracting giardiasis at that time in CO, let alone any water-borne disease.

Whether it's closer to 1/20 or 1/200 per year for someone who backpacks extensively and routinely drinks unpurified water, I don't think anyone knows.

Perhaps some day, one of the physicians in Mammoth Lakes or a similarly ideal location will lead a systematic study.

Best,

Bill S.

Katy Anderson
(KatyAnderson) - F
re water quality comparisons on 09/19/2012 22:49:42 MDT Print View

Thanks Bill, this explains something I could not quite wrap my head around.

Hetch Hetchy water comes from the Tuolomne river, pretty typical High sierra water.
That water is NOT FILTERED, but it is treated and that treatment in 2003 was chlorine, and then the water was piped to the residents of San Francisco.

If chlorination as you say leaves the Giardia cysts in place but renders them not viable, then a cyst count of the treated water would yield a fairly accurate count of the average Giardia cyst count in High Sierra water. As luck has it that treated Hetch Hetchy water heading for the residents of San Francisco is carefully analyzed and the results published in yearly reports for all to see.

According to the 2003 Rockwell study in 2001 there were 0.12 cysts / liter in San Francisco water. This pretty close to the highest level recorded in the Sierra in 1984 at Susie Lake south of Lake Tahoe, which measured at 0.108 cysts per liter.

But that never made sense to me, why would the San Francisco water, mainly coming out of High Sierra Hetch Hetchy water, be ever so slightly dirtier than the most polluted High Sierra Lake?

The answer became obvious when I read the City of San Francisco Water Quality Data for the Year 2011 report. http://sfwater.org/Modules/ShowDocument.aspx?documentID=2411

This shows the range of levels detected are from ND (none detected) to 0.07 cysts per liter. Max detection values where 0.07 Giardia cysts per liter for 2011.

So when the Rockwell study shows 0.12 cysts per liter for San Francisco water that is a MAX of 0.12 cysts per liter recorded in 2001. The number is almost identical to the MAX recorded cysts count per liter in the Sierra at Susie lake at 0.108 in 1984.

Now it makes more sense. The MAX Giardia cyst count measured in the High Sierra is pretty close to 0.1 cysts per liter whether measured at a lake or at the Hetch Hetchy reservoir.

So this still leaves open the question: "Is 0.1 Giardia cysts per liter something we really ought to filter out or not?"

PS. A slight wrinkle to this is that sometime between 2001 and today the SF Public Utilities Commission switched purification methods from Chlorine to Chloramine.
If Chloramine also leaves the Giardia cysts in place but yields them not viable then argument still stands that the SFPUC annual reporting of maximum Giardia cysts measured in Hetch Hetchy water is a good measure of Giardia contamination levels in the High Sierra.

William Segraves
(sbill9000) - F - M
Re: re water quality comparisons on 09/20/2012 04:45:40 MDT Print View

Good research, Katy - thanks!

Best,

Bill

Sean Heenan
(roadster1) - M

Locale: Southeast mountains
hetch hetchy water on 09/20/2012 07:02:40 MDT Print View

Seems they just started to use UV also.http://www.sfexaminer.com/local/2011/07/hetch-hetchy-water-goes-through-ultraviolet-rinse

Tom Kirchner
(ouzel) - MLife

Locale: Pacific Northwest/Sierra
Re: re water quality comparisons on 09/20/2012 17:13:15 MDT Print View

"then argument still stands that the SFPUC annual reporting of maximum Giardia cysts measured in Hetch Hetchy water is a good measure of Giardia contamination levels in the High Sierra."

This seems a bit of a stretch to me. For one thing, Hetch Hetchy is at a much lower altitude than much of the Sierra, which makes it a much less harsh environment for just about any aquatic organism, in terms of temperature range and UV exposure. Also, the same environmental considerations plus more vegetation would likely increase the density of critters serving as vectors for giardia. I am always leery of drawing broad conclusions from limited data, especially when conditions vary so widely in the Sierra. For instance, the giardia concentration in the LA aqueduct, which sources water from the eastern slopes of the Sierra, measures only .03 cysts/liter.

www.sierranaturenotes.com/naturenotes/Giardia.htm

If this link has not already been cited in this thread, I would highly recommend reading the report. It makes far more sense to me than anything I have ever come across on the subject.

Bill Law
(williamlaw) - M

Locale: SF Bay Area
giardia concentrations in Sierra H2O on 09/22/2012 19:53:34 MDT Print View

I recalled a local (SJMN?) news story a few years back about a perfessor who was measuring pathogens in Sierra water, going back yearly at numerous locations.

I didn't find the story, but did find the guy who I think was mentioned in the article: Dr. Robert Derlet, PhD.

There's some interesting stuff on rei.com, of all places (the number one profiteer on water purification systems, I'll wager): http://www.rei.com/learn/expert-advice/water-researcher-QA.html.

Also, another article he authored (not a research paper, by any means): http://www.pcta.org/help/join/magazines/SierraWater.asp

That article mentions that they couldn't find giardia cysts in the manure of Sierra pack animals, which I found surprising. In the REI page, Derlet says he would treat water downstream from cattle grazing. But perhaps that's due to concerns over coliform or other bacteria.

I haven't actually found any quantitative reports from his giardia-counting efforts, save for the "you'd have to drink 250 liters to get sick" statement, which maybe implies one cyst per 25 liters, or .04 cysts/liter, assuming he's using the "10 cysts minimum myth. I'll concede that the 10-cyst thing is a bit of a myth. Note that that does not invalidate the hard number contained therein: .04 cysts per liter.

There seems to have been much discussion here, in the past week, of the question of how to interpret the words of the one Colorado study. It has been claimed that Rockwell's paper has been "debunked." Has anybody tried to debunk that Colorado study?

It seems easy to pick nits with details in any study or article. I will go back and try to re-read the debunkification of the Rockwell paper. But has his basic thesis been debunked? That might be summed up as:
1. Giardia is everywhere. Has that been debunked?
2. There isn't (much) giardia in Sierra streams. That seems bunked, still, so far as I can tell. See Derlet, above.
3. You aren't likely to get giardia from drinking the water. Has that been debunked? How do you reconcile that with the absence of giardia in the water (assuming that's not debunked). See also articles to the contrary (e.g., "Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness, Lake Tahoe").
4. If you get giardia, you likely won't even know it. I've cited one study already that supports that claim.
5. If you get sick, it is most likely something else. See the paper cited under 3.

While one can pick holes in specific statements in the midst of this argument, that doesn't mean that the argument doesn't still hold up. The flip side of "even a stopped clock is right twice a day" is that "even an argument with a couple of flaws can still lead to a valid conclusion."

Perhaps the OP's biggest mistake was the admonition "Let's talk SCIENCE." It's not really a scientific question. It's a question about the level of risk one is willing to accept.

BTW, somebody above said: Still unanswered, my original question that started my readings: how long does a giardia cyst live in the air, out of water or outside of fecal matter?

That very question is answered plainly enough in the very report that has been roundly criticized (and allegedly "debunked") here. Most loudly, ironically, by the guy who asked the question. I wonder if he even read that report.

Here are the citations for that particular detail (I won't repeat the "debunked" answer to the question; look it up yourself).

15
DeReigner D. P., et al: Viability of Giardia Cysts Suspended in Lake, River, and Tap Water. Applied Environmental Microbiology, Vol. 55 no. 5, 1989
16
Olson, M. E: Human and Animal Pathogens in Manure. Conference on Livestock Options for the Future. Winnepeg, Manitoba, June 2001

William Segraves
(sbill9000) - F - M
Re: giardia concentrations in Sierra H2O on 09/23/2012 09:31:55 MDT Print View

"It's not really a scientific question. It's a question about the level of risk one is willing to accept."

I agree wholeheartedly with the second sentence, but whether I’m willing to accept a 5% risk/year or a .05% risk/year, I have to have some way to make a meaningful estimate of the risk in order to make a rational decision. The only way I know to do that is to look at the science.

A casual reading of Rockwell’s analysis might lead one to believe that the risk of contracting giardia from drinking untreated Sierra water during an extended trip would be on the order of 1 in a quadrillion. Depending on how one interprets the data, that may be off by around a factor of ten trillion. In my acceptable risk range, this turns out to make a difference. (N.b., it didn't have to turn out that way - if that 1 in a quadrillion had only turned into 1 in a million on further analysis, I wouldn't have to care.)

Best,

Bill S.

Edited by sbill9000 on 09/24/2012 18:08:31 MDT.

Buck Nelson
(Colter) - MLife

Locale: Alaska
The debunking of the giardiasis "science" on 09/27/2012 20:44:53 MDT Print View

Hi Bill,

Only by establishing some baseline scientific facts can a rational risk assessment be made.

I think the Rockwell paper has been solidly debunked. Not nitpicking at little points, but the very heart of the report:

Rockwell says"
*Giardiasis is "an extraordinarily rare event" in backpackers. False. It's common.
*"The minimum infectious dose is ten cysts." False.
*(to paraphrase) "It would be nearly impossible to drink enough water in the Sierras to contract giardiasis." False. You could get it with one drink. (Plus the study is decades old.)
*Rockwell says “Almost always, Giardiasis goes away without treatment”
and “If you get a Giardia infection, you are unlikely to have
symptoms.” The Colorado survey of 256 infected people showed they were sick an average of 3.8 weeks and lost an average of about 12 pounds. AVERAGE.

Here's a quote from a newspaper article from a recent Derlet Sierra water survey:
http://www.modbee.com/2010/05/08/1158938/fouled-waters-sierra-lakes-streams.html#
Nowhere is the water dirtier, he discovered, than on U.S. Forest Service land, including wilderness areas, where beef cattle and commercial pack stock — horses and mules — graze during the summer. There, bacterial contamination was easily high enough to sicken hikers with Giardia, E. coli and other diseases. Rockwell tells us to "drink freely" in the Sierras.

I have never seen where someone has tried to debunk the Colorado study we've discussed.

I'm not sure who is saying "giardia is everywhere." The EPA has said Cysts have been found all months of the year in surface waters from the Arctic to the tropics in even the most pristine of surface waters I don't think they literally mean ALL waters, just in a surprising variety of surface waters.

Even the Rockwell surveys show that there was giardia in 1/3 of the sources tested in the Sierra. If the true minimum infectious does is 1-10 cysts that's enough to make a whole lot of people sick. And those tests are OLD.

You aren't likely to get giardia from drinking the water. Has that been debunked? Yes. It was a speculative claim to begin with. The Colorado survey alone shows drinking untreated water increases the giardiasis risk by 5 times according to a post above.

Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness, Lake Tahoe does not prove what some people claim it does. It showed from 5.7 to 8.5% of backpackers got giardiasis on one trip and that there was giardia in the local water. It did not prove where they got their giardiasis but inferred it couldn't have been from the water due to the "10 cysts minimum infectious dose" myth. That has been debunked. Also unless the water they actually drank was tested, and it wasn't, there is no way of knowing how much giardia was in the water they actually ingested.

If you get giardia, you likely won't even know it. I've cited one study already that supports that claim. I think that's true. But if you get sick with it, you'll likely get very sick indeed. See the 3.8 weeks/12 pound weight loss quote above. Those people definitely noticed it.

"even an argument with a couple of flaws can still lead to a valid conclusion." The Rockwell article and the Welch papers don't have "a couple of flaws." The central points of their conclusions don't stand up to scrutiny. See the below if you'd like to try to refute specific points I've made.

I think it's interesting that Rockwell says "Cysts can survive for as long as 2 to 3 months in cold water, but they cannot tolerate drying" yet argues people aren't getting giardiasis from drinking water, but from dirty hands.

Debunking the "Giardia Myth"
Debunking a Welch Giardia Aricle

Edited by Colter on 09/28/2012 12:54:00 MDT.

Bob Shaver
(rshaver) - F

Locale: West
My experience on 09/27/2012 21:36:05 MDT Print View

I've hiked a lot, or at least for a long time: 40 years. I've never had giardia, but my partner got it on a trip to the North Cascades, drinking out of the same water sources as me. He definitely did not get an e coli infection from hygeine issues. He was sick for weeks, and weak for months, and I don't think he ever regained the muscle mass he lost.

After that I almost always filter water in the backcountry.

That is my only statistic, I have not done a survey or anything.

Paul Johnson
(johncooper) - F

Locale: SoCal
Rockwell report and Giardia:Let's Talk Science on 09/28/2012 15:09:58 MDT Print View

Bruce,

Has someone debunked Rockwell or is your statement "I think the Rockwell paper has been solidly debunked." simply based on the comments you are making?

I find the Rockwell study well written, data driven and well supported by references.
For reader convenience http://www.ridgenet.net/~rockwell/Giardia.pdf

If you want to debunk Rockwell, and do it under your thread of "Giardia: Let's Talk Science", then can you provide data or science to refute Rockwell's data?

I find his data regarding Giardia concentration in the Sierra's and his references to studies showing that 10-25 cysts per liter are needed to have a reasonable (1/3) likelihood of contracting Giardia to be compelling.

"The highest concentration of Giardia cysts (in 69 Sierra locations) was 0.108 per liter of water in Susie Lake, south of Lake Tahoe. The next highest was 0.037 per liter near Long Lake, southwest of Bishop. Samples taken in the Mt. Whitney area varied from 0 (most sites) to 0.013 (Lone Pine Creek)"

"Summary figures
Units are cysts per liter.
Concentration Comment
~1000 Typical swimming pool contamination
~100 Giardiasis is plausible
~10 Minimum needed to contract giardiasis
~1 Some wilderness water outside California
0.12 Some San Francisco water
0.108 Worst Sierra Nevada water
0.030 Some Los Angeles Aqueduct water
0.013 Mt. Whitney at Trail Camp
0.003 Mt. Whitney at Whitney Portal"

Per the earlier posts, most of us are trying to make a risk assessment. These low concentrations lead to an assessment to drink untreated Sierra water. Especially, if you practice BPL self styled "good" sources criteria.

William Segraves
(sbill9000) - F - M
Re: Rockwell report and Giardia:Let's Talk Science on 09/28/2012 16:11:57 MDT Print View

For any who are still game, let's go back to some of the key science:

1) What does the relevant scientific study say about whether you can get giardiasis from ingesting one cyst?

2) What does Rockwell say about whether you can get giardiasis from ingesting one cyst?

3) Upon what key assumption does Rockwell's analysis of the probability of contracting giardiasis from drinking lightly contaminated water depend?

Best,

Bill S.

Paul Johnson
(johncooper) - F

Locale: SoCal
Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/28/2012 19:02:15 MDT Print View

From the Rockwell report.

"How many cysts does it take to get the disease? Theoretically, only one. But there are no documented cases of giardiasis being contracted from such low levels. Volunteer studies have shown that 10 or more are required to have a reasonable probability of it, with about one-third of persons ingesting 10 – 25 cysts getting detectable cysts in their stools. 9, 10, 11, 13, 41, 42"

9
Juranek, Dennis D.: Giardiasis. Centers for Disease Control and Prevention, 1990
10
Swartz, Morton N.: Intestinal Protozoan Infections. Scientific American Medicine, 1994
11
Kerasote, Ted: Great Outdoors; Drops to Drink. Audubon, July 1986
13
Backer, Howard D.: Giardiasis: An Elusive Cause of Gastrointestinal Distress. The Physician and Sportsmedicine, Vol. 28 no. 7, July 2000
41
Ortega, Y.R. et al: Giardia: Overview and update. Clinical Infectious Diseases, Vol. 25, 1997
42
Rendtorff, R: The Experimental Transmission of Human Intestinal Protozoan Parasites. American Journal of Hygiene, Vol. 59, 1954

Buck Nelson
(Colter) - MLife

Locale: Alaska
My opinion doesn't debunk Rockwell, the science does on 09/28/2012 19:26:04 MDT Print View

One thing that makes the Rockwell paper dangerous (and it was dangerous enough for me personally that I ended up at a hospital) is that it cites so many scientific papers that it's easy to conclude that the conclusions are scientifically supported. But I believe my blog posts, which reference many of those same scientific papers, show that most of Rockwell's main conclusions simply aren't supported by the underlying science.

John Cooper, please read through my two blog posts cited above because otherwise I'm presenting my case in bits and pieces. If you had read through them you'd see why the seemingly impressive Rockwell cyst count data is extremely misleading.

Bill S., I like the way you think. The answers to #2 and #3 are clear. At least one statistician has told me that the answer to #1 would be "not enough data to draw a reliable conclusion."

William Segraves
(sbill9000) - F - M
Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/28/2012 19:35:10 MDT Print View

I have read Rendtorff in full, but not all of the others. Are any of the others independent experiments, or all just references back to Rendtorff?

Bill S.

William Segraves
(sbill9000) - F - M
Re: Rockwell report and Giardia:Let's Talk Science on 09/29/2012 05:18:17 MDT Print View

John,

While I and others work on whether the other references provide any independent info, may I ask two more questions?

You wrote "I find his data regarding Giardia concentration in the Sierra's and his references to studies showing that 10-25 cysts per liter are needed to have a reasonable (1/3) likelihood of contracting Giardia to be compelling. "

Did you mean to say "10-25 cysts per liter"?

Is a 1-3% likelihood during any given trip a "reasonable" likelihood, or something that you would say no one needs to be worried about?

Best,

Bill S.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/29/2012 05:54:37 MDT Print View

And it's wise to remember that the only two cited before/after studies I could find showed at least 5% of people were picking up giardiasis on a single camping trip.

So far "all roads lead to Rendtorff" for infectious dose experiments. As has been said, that experiment does not support Rockwell's 10 cysts minimum for an infectious dose claim which is a cornerstone of his whole paper.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/29/2012 15:35:05 MDT Print View

> showed at least 5% of people were picking up giardiasis on a single camping trip.
I am willing to believe that giardia cysts can be found in the wild in some places - I KNOW they are there (in some places) from personal experience.

But the idea that AT LEAST FIVE PERCENT get giardia from a single camping trip??????? That I simply do NOT believe. No way at all. Our Forum threads would be drowing in reports. They aren't.

Question: did those studies actually check faecal matter for giardia cysts by microscope every time, or did they just believe the walker's claims? I have my suspicions.

Cheers

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/30/2012 05:29:12 MDT Print View

Roger,

It seems obvious you still haven't read what I've written. I've got clickable links above at 09/27/2012 20:44:53.

From the first study: Twenty-five...campers had stools examined before and after a subsequent hiking trip in another area of Utah; none had Giardia cysts before, but 6 (24%) had them after return

A quote from my post about study #2, which also tested campers before AND after their trip:

[Welch] goes on to say: "An excellent effort at such a study, however, was recently reported by ZelI and Sorenson [17]. Although 16% of a cohort they studied developed transient gastrointestinal illness following a visit to an area of high use, none developed symptomatic giardiasis." I agree that it is one of the very best studies of it’s kind. However, what Welch doesn’t say is that one person was empirically diagnosed with giardiasis, was treated, and quickly recovered. Giardia is often not detected with a single test. Two more people tested positive for giardia but were asymptomatic at the time of the last test. About 2/3 of Giardia carriers are asymptomatic which would match this study exactly. So it is certain at least 5.7% got Giardiasis, and it seems more than likely that 3 of 35 got giardiasis, for a total of 8 1/2%. On a SINGLE TRIP. To me, Welch went far beyond a little spin in trying to make a point.

A major goal of these studies was to see if people actually WERE getting giardiasis in the wild. Skeptics were arguing there was no proof it was happening. They argued that "it probably wasn't giardiasis" and "almost no one gets tested." They still do so even after these studies were done.

See this poll

In that poll almost 22% have had giardiasis. Almost half of those cases were confirmed by lab tests.

Edited by Colter on 09/30/2012 05:35:55 MDT.

William Segraves
(sbill9000) - F - M
Re: Rockwell report and Giardia:Let's Talk Science on 09/30/2012 10:36:25 MDT Print View

With apologies to those for whom this may be review, let's go back to the question of what the relevant scientific literature says about whether you can get giardiasis from ingesting one cyst and the six papers that were cited above.

* Juranek, Dennis D.: Giardiasis. Centers for Disease Control and Prevention, 1990


This is no longer available on the CDC website. Current references on the CDC website all go back to Rendtorff (see below).

* 
Swartz, Morton N.: Intestinal Protozoan Infections. Scientific American Medicine, 1994


I do not have access to this, but it appears to be a collection of reviews, not original research.

* Kerasote, Ted: Great Outdoors; Drops to Drink. Audubon, July 1986


Kerasote is an author. I don't have access to the article, but it seems reasonable to expect that this was not a publication describing independent experimental investigation of infectivity. If anyone really doubts this, we could ask him.

Backer, Howard D.: Giardiasis: An Elusive Cause of Gastrointestinal Distress. The Physician and Sportsmedicine, Vol. 28 no. 7, July 2000

This is a review, to which I do not have full text access, but as a review, it would not normally be expected to contain new experimental findings, and there is nothing in the abstract to indicate new findings by the author.

FWIW, the abstract concludes by saying ”Prevention for people involved in outdoor sports or recreation and for international travelers includes treatment of all surface water and rigorous personal hygiene.”

* Ortega, Y.R. et al: Giardia: Overview and update. Clinical Infectious Diseases, Vol. 25, 1997


Ortega and Adam is a review article, which I have read. They are commendably circumspect in their interpretation of Rendtorff's findings: “Infections may result from the ingestion of 10 or fewer Giardia cysts."

FWIW, their concluding statements include “Since G. lamblia is frequently found in lakes and streams —
even in remote areas — hikers and backpackers should be warned to boil or filter water prior to ingestion.”

* Rendtorff, R: The Experimental Transmission of Human Intestinal Protozoan Parasites. American Journal of Hygiene, Vol. 59, 1954

In the absence of evidence to the contrary, it appears that this is the only paper that investigated infectious dose. 0/5 people who got one cyst were infected (subsequently showed cysts in their stools). 2/2 people who got 10 cysts were infected. 6/20 who got 25 cysts were infected.

That's it - the sum total of all the scientific evidence as to whether a low number of cysts can cause infection. Maybe it's my own biases, but when I hear things like "theoretically possible," I'm thinking maybe one in a thousand, or even one in a million. Things that people have looked very hard to find. What does five people tell us? Suppose, for a moment, that the real rate infection for a single cyst is 10% (if I had to bet, I'd bet it's lower, but let's just suppose that for a moment). Could Rendtorff have expected to see an infection among just five people? Nope, he would have had a better chance of getting a hit by spinning a roulette wheel and picking red or black.

He doesn't deal with it explicitly, but Rendtorff understood this. His conclusions had to be based only on what he *had* seen, and he wrote in his conclusions, “The fact that only a few cysts will establish the infection indicates that avenues of infection where it is probable that only a small number of cysts would be transferred may be of importance.”

William Segraves
(sbill9000) - F - M
interpreting the data on giardia risks on 09/30/2012 11:51:19 MDT Print View

I'm not looking to dissect every potential flaw in Rockwell's and similar assessments of Giardia risks, but I do think it's valuable for people to understand that there are some common misconceptions and misunderstandings that can arise from a casual reading of it *and* other writings (on both sides of arguments as to whether Giardia should be a major concern for backpackers) that deal with the subject.

If you read Rockwell, for instance, as saying that you're probably not going to get giardiasis from a given drink of reasonably well-selected Sierra water, then you need read no further.

But if you read it as saying any of the following, caveat emptor:

1) If you read it as saying that a significant body of scientific evidence shows that if you haven't ingested at least 10 cysts, your chances of getting giardiasis are effectively nil, you might want to look at the evidence. There's one paper, with five people who were given one cyst each. Five people.

2) If you read through a set of calculations quantifying your astronomically low chances of ingesting 10 cysts within given amounts of water, you might want to look at whether those are the right calculations. Is 10 cysts really the right number to be using (see above)? Even if there is a threshold, should we be making calculations as if cysts are randomly distributed? (Credit to Rockwell for pointing out this caveat himself.) Even if there is a threshold, are there any relevant data as to the time-frame within which the cysts must be consumed? Even a few tens of liters sounds like a pretty ridiculous amount to drink, unless you're talking about a week or two.

3) If you read it as saying that untreated Sierra water is safer than what millions of people in SF and LA drink, you might want to look at the evidence. That SF and LA water has been treated in ways that inactivate some proportion of the cysts (potentially a very large proportion of the cysts, depending on some details that are not readily available) so that they're not infectious.

If I've misinterpreted the state of scientific evidence wrt any of these three things, I welcome having those misinterpretations pointed out and look forward to re-examining these issues. In the course of this discussion, I've learned quite a few things I didn't know, and I am eager to learn more.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/30/2012 11:55:44 MDT Print View

Thanks sbill9000 for all the hard work. Again, that's the kind of data-based discussion I wanted to see here.

Seemingly convincing quotes like the one below are extremely misleading because they use bogus infectious dose numbers. They are also based on dated studies done in limited areas.

...of those sources that had cysts present, the amount was ridiculously low – nowhere near enough to make you sick, considering you must ingest approximately twenty viable cysts to develop giardiasis...Therefore, you would have had to
drink 132 gallons of untreated Sierra Nevada water in 24 hours to get giardiasis...
(Giardia Myth-Buster: How Rumor and Paranoia Have Created a False Industry Standard) [my bold]

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Rockwell report and Giardia:Let's Talk Science on 09/30/2012 12:41:24 MDT Print View

Another thing is that the whole focus here seems to be on cysts. There are trophozoans as well. Of course they are much easier to filter out, but if they get in you, you can get sick.

I can see this coming. In a few years we will be trying to do DNA testing on giardia cysts.

--B.G.--

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/30/2012 19:13:07 MDT Print View

Hi Buck

First of all, please remember that a few anecdotes do not make for credible science, even if they are true. It is far too easy to cherry-pick such data, and that happens all the time. Very often it is not even intentional.

> From the first study: Twenty-five...campers had stools examined before and after a
> subsequent hiking trip in another area of Utah; none had Giardia cysts before, but
> 6 (24%) had them after return
I took this to mean they were all on one trip. OK, so that's one case where giardia was spread. However, I wonder where it came from? Perhaps there was an asymptomatic carrier in the party, and a general lack of hygiene on everyone's part led to others getting Giardia from him? An entirely believeable scenario, but valueless for scientific purposes.

> Although 16% of a cohort they studied developed transient gastrointestinal illness
> following a visit to an area of high use, none developed symptomatic giardiasis."
I would interpret that in the same way: E coli infections spread from one person by poor hygiene. Happens all the time.

> what Welch doesn’t say is that one person was empirically diagnosed with
> giardiasis,was treated, and quickly recovered.
Empirically? They guessed? And the gastro infection went away in the few days while he was being treated for Giardia? Entirely believable, common for gastro, but certainly NOT a proof of Giardia.

> So it is certain at least 5.7% got Giardiasis, and it seems more than likely that 3 of 35 got
When I see a figure like 5.7% quoted for a study involving just 35 people, I get very cynical. With 35 people you can't have an accuracy any better than ~3%, so quoting to one decimal place is futile.

> In that poll almost 22% have had giardiasis.
A meaningless result. What happens in such polls is that the only respondants are those who thought they did get Giardiasis. The vast majority who did not get sick don't bother to reply. It might make good headlines, but it is not science.

Sorry, but ...
Cheers

Edited by rcaffin on 09/30/2012 19:15:23 MDT.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: interpreting the data on giardia risks on 09/30/2012 19:15:18 MDT Print View

Good stuff as usualsbill9000. You said:

3) If you read it as saying that untreated Sierra water is safer than what millions of people in SF and LA drink, you might want to look at the evidence. That SF and LA water has been treated in ways that inactivate some proportion of the cysts (potentially a very large proportion of the cysts, depending on some details that are not readily available) so that they're not infectious.

The reality is the SF/LA city water is going to be far, far safer than random untreated Sierra water.
Beginning in 2011, UV light will be implemented for primary disinfection of
Hetch Hetchy water source in addition to chlorine. Second, chloramine is formed to prevent microorganisms from growing in the pipes, which distribute water to the customers.
http://www.sfwater.org/modules/showdocument.aspx?documentid=960

Here's how Rockwell put it: the US Environmental Protection Agency and the California Department of Health Services have granted Hetch Hetchy water a filtration exemption, meaning that filtration treatment to ensure its safety from Giardia and other organisms is not required

Makes it sound like the raw water is safe as is so Sierra Mountain water must be safer yet. That's clearly not the case.

Here's how the Metropolitan Water District of Southern California treats it's water:

1.Screening with relativelly coarse sieves removes larger debris such as sticks and leaves.
2.Primary disinfection with chlorine. Several of Metropolitan's treatment plants are now using ozone instead of chlorine as a primary disinfectant.
3.Addition of flocculant chemicals such as ferric chloride and organic polymers to encourage smaller particles to clump together.
4.Sedimentation to allow the clumps to settle out of the water.
5.Filtration to remove remaining particles.
6.Next, more chlorine is added to the water to disinfect and prevent any illness due to water-borne pathogens.
7.Lastly, ammonia is added to the water to react with the chlorine to form chloramines. Chloramines are used to maintain a residual disinfectant throughout the water distribution system.
8.After purification, sodium hydroxide is added to adjust the pH level to protect the pipes and plumbing fixtures, and fluoride is added to the water to help prevent dental caries in children.


http://en.wikipedia.org/wiki/Metropolitan_Water_District_of_Southern_California#Purification_and_treatment

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: Re: Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/30/2012 19:45:52 MDT Print View

Roger,

My two cited scientific studies are not cherry-picked anecdotes so please don't refer to them as such.

You said: I took this to mean they were all on one trip. OK, so that's one case where giardia was spread. However, I wonder where it came from? Perhaps there was an asymptomatic carrier in the party, and a general lack of hygiene on everyone's part led to others getting Giardia from him? An entirely believeable scenario, but valueless for scientific purposes. Pure speculation on your part about hygiene. The scenario is perfectly valuable scientifically because it directly refutes your opinion But the idea that AT LEAST FIVE PERCENT get giardia from a single camping trip??????? That I simply do NOT believe. No way at all

You said Empirically? They guessed? And the gastro infection went away in the few days while he was being treated for Giardia? Entirely believable, common for gastro, but certainly NOT a proof of Giardia. Nobody said it was proof for that single case. And yes, the physician "just guessed." Based on years of medical school and subsequent experience. That's why I called it empirically treated. Of course, the other two people had lab confirmed giardiasis, (5.7% of the group) which also refutes your opinion But the idea that AT LEAST FIVE PERCENT get giardia from a single camping trip??????? That I simply do NOT believe. No way at all

You said > [In that poll almost 22% have had giardiasis.]
A meaningless result. What happens in such polls is that the only respondants are those who thought they did get Giardiasis. The vast majority who did not get sick don't bother to reply. It might make good headlines, but it is not science

78% percent of responsdents said they have never had giardia, thus refuting your statement. The poll also refutes your earlier statement "very rarely is the patient actually tested for the presence of giardia cysts." If it's not science, it certainly is of more value than any single person's usubstantiated opinion, including mine.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: Re: Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 09/30/2012 19:58:39 MDT Print View

"My two cited scientific studies are not cherry-picked anecdotes so please don't refer to them as such."

Buck, if you read Roger's words more carefully, he did not refer to your anecdotes as cherry-picked.

--B.G.--

a b
(Ice-axe)
An account of my clinically diagnosed Giardiasis. Warning: GRAPHIC DETAILS on 09/30/2012 20:25:14 MDT Print View

I can add a little something regarding clinical diagnosis of Giardiasis.
I warn you though.. IF YOU ARE EATING OR ABOUT TO EAT DON"T READ THIS NOW!

In 2009 while on a long hike i contracted an intestinal illness.

The first symptoms were loss of appetite(despite hiking 25 miles per day), lethargy, and uncontroled diarhea with greasy black stools.
The first symptoms lasted a few days and lessened but returned again even stronger with new symptoms.
After ten days there was sulphurous gas, bloating, intense stomach cramps, clear mucousal diarhea and severe weightloss and dehydration.

After 20 days I had lost 30 lbs and the symptoms became so severe i sought medical help.

When i described the symptoms to the doctor one symtom caused him to clinch his diagnosis: Acute Giardiasis and perscribe metronidazole(Flagyl) right there on the spot without a fecal test.

That symptom was the clear, thick, mucousal discharge of diarhea.
The night before i went to the clinic i was hunkered down in my tent on the ski slope above hwy 50 in Tahoe.
I got up to relieve myself for the 10th time that hour and when i squatted down I filled the hole I had dug but could not stop the flow in time to dig another hole.
I estimate nearly a gallon of clear mucous came out of my body.
It really scared me.

The doctor said that in the acute phase the Giardia parasites can colonize nearly the entire small intestine.
The mucous they secreted combined with anything i ate or drank literally went right through me undigested.

okay.. here is the REALLY gross part and also the final factor in his clinical (best guess) diagnosis:
I had lost so much weight i forced myself to eat macaroni and cheese that final night.
The following morning I passed that macaroni and cheese and it was the same color and texture as if i had simply poured it out of my cup even after passing all the way through my gi tract.
Giardia had completely coated my intestine in mucous and nothing could get through.. i was starving.

My case was extreme. Most cases are not that cut and dried he said.

After 4 days on the Flagyl I was eating normally and back on trail.
By day 5 i got to the Soda Springs store near Donner pass and ate over 15,000 calories of food at one sitting.
By the end of that long hike I had regained all 30 lbs.

But Roger is quite correct. Neither that doctor or I can confirm scientifically that Giardiasis was what i had.
Thankfully for me though i did not have to wait 5 days or more for a test result before starting the antibiotic that brought about much needed relief.

I mention all this to il;lustrate that there are some pretty horrific symptoms related to Giardiasis that are far beyond your average case of E Coli poisoning.

Just to leave you with one final lovely detail... Immodium controlled the diarhea alright.. during the day that is.
Imagine a gallon of mucous spilling out from "down there" into your sleeping back in the middle of the night.

Any takers on a "slightly" stained and mysterious smelling WM ultralight?
To quote the Monkeys.. "I'm a believer"..

Edited by Ice-axe on 09/30/2012 20:34:30 MDT.

Franco Darioli
(Franco) - M

Locale: Melbourne
Giardia: Let's Talk SCIENCE on 09/30/2012 20:40:45 MDT Print View

Perhaps there was an asymptomatic carrier in the party, and a general lack of hygiene on everyone's part led to others getting Giardia from him?
That is why I don't share food on the trail, however I see that most do and that is of the "dunk your hand in the same bag and pick up some nuts" type sharing.
BTW, having drunk water from mountain creeks all of my youth (cows,sheep,goats,horses drunk and pooped in there too...) it is possible that I am a carrier so better not take food from me either.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: An account of my clinically diagnosed Giardiasis. Warning: GRAPHIC DETAILS on 09/30/2012 20:41:02 MDT Print View

Matthew, you are correct with your warning to us.

"Thankfully for me though i did not have to wait 5 days or more for a test result before starting the antibiotic that brought about much needed relief."

Maybe it takes five days or more for a microscopic test result from some state-certified lab. However, I watched while one physician peered through a microscope at a slide for only a few minutes before concluding a diagnosis of giardia. Sometimes the symptoms are slight, and they have to look for a while to find cysts. But, as the symptoms become more serious (like yours) the population of cysts becomes more overwhelming in the microscope slide, so they become quicker and easier to estimate and identify.

--B.G.--

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Giardia: Let's Talk SCIENCE on 09/30/2012 20:54:47 MDT Print View

Same here - seldomly share food or water - I have my allocated food so if I ate someone else's or they ate mine I wouldn't have the right amount of food.

"it is possible that I am a carrier so better not take food from me either"

I may be an asymptomatic carrier also

I think contamination is from your other end, and there are other bad organisms there so you want to use good hygene regardless : )

a b
(Ice-axe)
Re: Re: An account of my clinically diagnosed Giardiasis. Warning: GRAPHIC DETAILS on 09/30/2012 20:57:18 MDT Print View

Actually a fellow thru hiker in 2009 actually had a confimed test. I wont reveal his name here but he was not the only one.

I drank unfiltered water all my life too up until the PCT.
I decided to use chlorine bleach drops for the SoCal section but i quit using them around Kennedy Meadows mile 704.

Personally I never shared food but that does not rule out the possibility of someone transitting it to me on trail.
A common practice among most thru hikers i saw share food was to only dump it into a persons hand.

I also began using a spoon to eat things out of my Fritos bag or ziplock.

Just got back from a 7 day sierra trip where i never filtered or treated so having had Giardiasis has not changed my behavior.
If i get sick to my stomach it's one thing, Giardiasis is totally on another level of "stomache ache".
I would say don't be afraid but if you are sick for more than a week, have stomach cramps, greasy or mucousal stool it becomes more than just sick from bad hygene.

Edit:
Ya know.. I just realized i probably scared away every single chick on the internet.

Edited by Ice-axe on 09/30/2012 21:00:04 MDT.

Manfred Kopisch
(Orienteering) - F
Personal experience in the High Sierra - yes you can get Giardiasis on 09/30/2012 21:12:18 MDT Print View

Last year I got Giardiasis - tested for and confirmed by my doctor. As the symptoms started a week after my return from a High Sierra trip during which I drank exclusively untreated water, my doctor suspects I caught it during my trip. That is of course not "scientific" proof that I contracted it in the High Sierra by drinking untreated water. But for me the experience has been unpleasant enough to now treat every drop of water. Most likely it is not necessary 99.x % of the times, but after my experience I won't second-guess any longer.

Manfred

James Castleberry
(Winterland76)
Personal experience in the High Sierra - yes you can get Giardiasis on 09/30/2012 22:16:28 MDT Print View

Ditto to what Manfred said. Happened to me this year in very similar circumstances. I too will be taking precautions in future.No repeat please!

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: Re: Re: Re: Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 10/01/2012 03:22:06 MDT Print View

Bob said "Buck, if you read Roger's words more carefully, he did not refer to your anecdotes as cherry-picked."

Roger's post following his "cherry-picked anecdotes" comment refers exclusively to my cited scientific studies, So I think that's exactly what he was insinuating.

I have cited numerous scientific studies and haven't been relying on anecdotal evidence, cherry-picked or otherwise, so I think it was an unfair comment regardless.

Those two "before and after" studies weren't cherry-picked among studies, either, they are the only two of the type that I could find.

Michael L
(mpl_35) - MLife

Locale: The Palouse
Re: Re: Re: Re: Re: Re: Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 10/01/2012 03:29:24 MDT Print View

Rodger can weigh in, but I read it as the studies cherry picked their data points, not that you cherry picked the studies.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Rockwell report and Giardia:Let's Talk Science on 10/02/2012 20:02:13 MDT Print View

It seems the scientific thing to do would be to give examples of cherry picking and a reliance on anecdotal evidence, regardless of what he meant.

Getting back to the actual science of the matter, is there anyone who still thinks the Welch paper Giardisis as a threat to backpackers in the United States: a survey of state health departments still stands up to scientific scrutiny? Specifically this statement: Thus, neither health department surveillance nor the medical literature support the widely held perception that giardiasis is a significant risk to backpackers in the United States. In some respects, this situation resembles that recently described by Campbell and Smith in reference to shark attacks [18]: an extraordinarily rare event to which the public and the press have seemingly devoted inappropriate attention.

I believe they are perhaps the two most misleading sentences in the whole debate. If you have read and disagree with my linked rebuttal, I hope you will do so in a logical manner such as Bill S and Katy (for example) have skillfully done above, with their different possible interpretations of data.

Michael L
(mpl_35) - MLife

Locale: The Palouse
Buck on 10/02/2012 21:35:38 MDT Print View

Well buck, I kind of think he did


The poll you linked is pretty much irrelevant. There is a huge self selection bias in such polls. Despite your claim that 78% saying they didn't get sick is evidence to the contrary, that just isn't the case. Sure a portion of the population will respond negatively, but what a poll like this usually sees is a much higher participation rate for those that were sick. So for example you might get a 25% participation rate for non sick people and a 75% participation for sick ones. This skews the results. That is why proper sampling is key.

That is just one part of the problem.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Buck on 10/02/2012 22:20:30 MDT Print View

You kind of think he did what?

You said "Despite your claim that 78% saying they didn't get sick is evidence to the contrary, that just isn't the case." Roger said that only those who think they've gotten sick respond to such polls. If 78% say they didn't get sick, Roger was wrong. I think my arguments from my blog posts stand without using that poll at all. If you disagree please tell us why.

The poll is not a scientific sampling, of course and there's no doubt there's some skewing. But despite what you might think, I think it's a lot more useful than the strings of anecdotes and personal opinions that normally comprise threads like this. Even IF it's skewed exactly to the degree you have guessed, it's still strong evidence that not treating water is risky and that many people ARE getting lab tested and that giardiasis is considerably more common than shark attack. It supports the peer reviewed papers.

The trouble is, despite the thousands of anecdotal stories from people who say they've gotten giardiasis from bad water, despite the polls, despite the CDC and EPA and the Mayo clinic saying its happening, despite the peer-reviewed scientific papers that agree, there will always be some people who won't believe it's happening and who will continue to try to cast doubt in any way they can, including focusing on peripheral evidence as much as possible.

So what do YOU think the science shows?

Edited by Colter on 10/02/2012 22:32:36 MDT.

Michael L
(mpl_35) - MLife

Locale: The Palouse
Re: Re: Buck on 10/02/2012 23:08:26 MDT Print View

First I think this is a great thread.


Second I think rodger pointed out problems is what I was saying:

The poll that is likely to have problems. So many in fact to make it useless.

The validity of the study on what appeared to be one group? Without identifying the cause we can only assume where it came from.

The extremely small sample sizes. Etc.


Third.

I agree that your point doesn't need the poll. I did think the point that people are getting tested some of the time is interesting. But we can't tell how often since we still have a selection bias.

Fourth.

I haven't formulated a final opinion yet. I do agree that people are getting sick. However we have such a wide array of information. You have people getting sick on one trip and thrus never getting sick despite months drinking untreated water everyday.

We don't have definitive info on how many cysts you need to get sick. Lots of questions still.



We need more good studies. But I'm not sure there is much funding. :). So I am really just soaking up the info still.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Conflicting evidence is standard on 10/03/2012 07:39:43 MDT Print View

For now I will cease beating a dead horse on most of your concerns. I have either made my point or there's little hope.

"You have people getting sick on one trip and thrus never getting sick despite months drinking untreated water everyday. "

As for your quote above, that's to be expected. 2/3 of people who get giardiasis, more or less, are asymptomatic. There are people who can beat the odds at just about anything.

Scott Williamson, Mr PCT himself: Williamson does not filter or treat his water. 'I’ve been sick multiple times, I have had giardia…' (and then he ticks off a list of other parasites, but your trusty reporter was too dumbfounded to write them all down).'I am very selective about my water. If it looks like a heavily used area I will try to find cleaner water, but I have had to drink some nasty water. It saves time, I just dip and drink.' He does add, 'If you don’t want to be sick at some point, you have to always treat your water.'

http://www.moonshineink.com/sections/sports-wrap/scott-williamson-unsung-super-athlete

I know some people will say cherry-picked, anecdotal, biased. Yet it is another piece of powerful evidence backing up the peer-reviewed science.

Edited by Colter on 10/03/2012 10:54:19 MDT.

Paul Johnson
(johncooper) - F

Locale: SoCal
Re: Conflicting evidence is standard on 10/03/2012 16:27:49 MDT Print View

Regarding
'If you don’t want to be sick at some point, you have to always treat your water.'

Actually that part has been studied and proven false.

"Mueser made contact with 136 thru-hikers. Some of them boiled their water,
some used a chemical treatment, some used a filter, and some did not treat their water at all. In each of these four groups, approximately one-quarter suffered gastrointestinal illness.

Mueser's data follows.
How often they treated their water Percent who became ill
Always 21%
Usually 28%
Sometimes 29%
Never 20% "

Paul Johnson
(johncooper) - F

Locale: SoCal
Re: Re: Conflicting evidence is standard on 10/03/2012 16:36:28 MDT Print View

In "Giardia Myth-Buster: How Rumor and Paranoia Have Created a False Industry Standard " By Erik Schlimmer, he makes the statement "Therefore, you would have had to
drink 132 gallons of untreated Sierra Nevada water in 24 hours to get giardiasis
(assuming every cyst was viable, which is highly unlikely)."

It appears he is using 24hrs as a viable cyst life within the human body. Does anyone in the forum have an understanding of cyst viability in the human body?

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: Conflicting evidence is standard on 10/03/2012 17:05:09 MDT Print View

Your referenced study is smaller than the following study and not peer reviewed.

This study was peer reviewed:

http://onlinelibrary.wiley.com/doi/10.2310/7060.2004.13621/abstract

Here is what that paper concluded:

Lack of hygiene, specifically handwashing and cleaning of cookware, should be recognized as a significant contributor to wilderness gastrointestinal illness. Hikers should routinely disinfect water and avoid untreated surface water.

However, in both studies giardiasis isn't specifically broken out.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Conflicting evidence is standard on 10/03/2012 17:34:13 MDT Print View

"Lack of hygiene, specifically handwashing and cleaning of cookware, should be recognized as a significant contributor to wilderness gastrointestinal illness. Hikers should routinely disinfect water and avoid untreated surface water."

You know that paragraph is inconsistent

On the one hand it says washing hands and cookware is the solution

On the other it says water treatment

But, it's so easy to use the Squeeze that I usually just do that. And my cookware never gets very dirty and I use one pot for everything and boil water the next time I use it. And I keep bad stuff off my hands.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Both water treatment and hygiene are important on 10/11/2012 15:41:29 MDT Print View

Actually I think that paragraph is consistent for that reason. It's not one or the other, it's both.

As has been mentioned, NOLS has seen various stomach ailments plummet with good hygiene, proper cooking/cookware practices, and water treatment.

Of course Giardiasis is a subset of gastro-intestinal illness in general.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Both water treatment and hygiene are important on 10/11/2012 15:45:51 MDT Print View

> Actually I think that paragraph is consistent for that reason. It's not one or the other, it's both.
+1

Cheers

Buck Nelson
(Colter) - MLife

Locale: Alaska
See the below post on 11/06/2012 07:49:09 MST Print View

Redundant post. See my below post.

Edited by Colter on 01/05/2014 10:03:34 MST.

Buck Nelson
(Colter) - MLife

Locale: Alaska
More giardia research on 01/05/2014 10:01:54 MST Print View

This thread is, I believe, by far the best discussion on giardia to every appear on any outdoors forum. I've done more research on the topic that addresses some of the questions we had.

On the giardia cyst count in San Francisco water: I talked to the water treatment authorities there and they said the cyst count was at the water INTAKE. In other words, raw water that hadn't been run through the treatment plant yet.

Since before the time the Rockwell paper was written, the national Surface Water Treatment Rule has been in effect. That means that the treated water people have been drinking in the city has had a MINIMUM of 99.9% of giardia cysts and 99.99% of viruses removed/killed. One of the most commonly quoted "facts": Sierra Nevada water has fewer Giardia cysts than, for example, the municipal water supply of the city of San Francisco is simply false.

The "minimum infective dose" for giardiasis is not 10 cysts which is often quoted, it's one cyst. There is about a 2% chance of being infected after ingesting a single cyst. The risk from ingesting more cysts is cumulative but only to a degree.

Risk assessment and control of waterborne giardiasis

There are other diseases sourced to untreated backcountry drinking water:
Campylobacter Enteritis from Untreated Water in the Rocky Mountains


Rockwell's errors in a nutshell

Some people get sick, some don't. I don't care if you treat your water or not. :)

Bill Law
(williamlaw) - M

Locale: SF Bay Area
Nelson's errors in a nutshell on 01/09/2014 00:47:04 MST Print View

Thanks for the update, Buck.

I few minutes of Googling produced some tidbits:

1. San Francisco does not filter its water from Hetch Hetchy (see 2012 SF Water Quality Report)

2. it did not use chlorine to treat its water during distribution until 2004 (Rockwell's paper seems to have been written prior to that); see here, and here

3. Chlorine has low to moderate effectiveness in killing Giardia (according to the CDC)

4. it did not use UV until 2011 (see this page).

5. SF water has somewhere between 0.01 and 0.06 giardia cysts per liter (2012 SF Water Quality Report, op cit), similar figures back to 2010. The figures for contaminants doesn't state explicitly that it is at the output, but that can be readily inferred, using either common sense (otherwise, the tests are sort of pointless) and from the fact that the source of chloramine is "the treatment process" which clearly means the samples don't come from the intake pipe.

6. Figures for the occurrence of giardia cysts in Sierra water is a bit harder to come by. But one reference ("Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness, Lake Tahoe") mentions "single digits for 100 gallons". That's on the order of <.03/L (if my math is correct).

7. There are also many somewhat anecdotal reports of tests of Sierra water that were giardia-free (which I suppose translates to <0.01 cysts/L). See, for example, this, and this

Absent more citations as to the prevalence of giardia in Sierra water with higher numbers, or, refutation of the facts in the SF Water Quality Reports, it seems a stretch to claim this is an "error" on Dr. Rockwell's part.

Bill

Edited by williamlaw on 01/09/2014 00:53:14 MST.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Nelson's errors in a nutshell on 01/09/2014 10:08:03 MST Print View

A few minutes of Googling is not enough.

San Francisco has been treating Hetch Hetchy water with Chlorine or Chloramine since long before Rockwell wrote his paper. In 2004 they switched from chlorine to chloramine.

In a controlled environment, like a modern treatment plant, over 99.9% of giardia cysts can be killed using chlorine or chloramine, (source: Optimizing Chloramine Treatment, Gregory Kirkmeyer, Kathy Martel) which is the safety level the Surface Water Treatment Rule standard requires, so your point about treatment effectiveness is invalid.

I DID talk personally to the water treatment officials and they told me the cyst level count was at the intake. But even if the testing IS done on the output, 99.9% plus (and 99.99%+ of viruses) of those cysts would be dead after treatment so Rockwell's point is invalid regardless.

It's silly to compare city water which is tested on an ongoing basis with a real-world water source which has likely never been tested in history and if it has, likely decades ago.

You quoted Derlet above. From a 2010 article Where do you get infections in the wilderness? The most obvious possibility, he believed, was the water.

Now, after 10 years of fieldwork and 4,500 miles of backpacking, Derlet knows for sure. What he has learned, after analyzing hundreds of samples dipped from backcountry lakes and streams, is that parts of the high Sierra are not nearly as pristine as they look.


Read more here: http://www.modbee.com/2010/05/08/1158938/fouled-waters-sierra-lakes-streams.html#storylink=cpy

Edited by Colter on 01/09/2014 10:19:23 MST.

Tom Kirchner
(ouzel) - MLife

Locale: Pacific Northwest/Sierra
Re: Re: Nelson's errors in a nutshell on 01/09/2014 15:58:54 MST Print View

"Now, after 10 years of fieldwork and 4,500 miles of backpacking, Derlet knows for sure. What he has learned, after analyzing hundreds of samples dipped from backcountry lakes and streams, is that parts of the high Sierra are not nearly as pristine as they look."

It was good to read this article again, Buck. Thanks for posting it.

I think the key word here is "pristine". The areas Derlet found to be problematic were basically overrun by cattle, certainly not pristine by any reasonable definition of the word. At the other end of the spectrum, he found almost all the water at higher elevations in the Sierra to be pure enough to drink without treating. At this point, he and Rockwell converge. It is a simple matter of using your powers of observation and your mind to make a determination as to whether or not to treat. Many of us have been doing this for years will no ill effects, which at least anecdotally confirms the findings of both Rockwell and Derlet. I don't think anyone in their right mind would drink water untreated under the conditions described by Derlet in cattle country. For me that also applies to choosing to hike in such places in the first places. HYOH, I guess, but live with the constraints and consequences if you do.

David Olsen
(bivysack.com) - F

Locale: Channeled Scablands
Hiking with a Vet on 01/09/2014 18:09:30 MST Print View

Hiked with a Vet from Florida. He said all the puddles everywhere in Florida were full of giardia and he continually treated dogs as they just kept the cycle going by drinking and pooing in the same places. When he saw the sheer volume of water from the 50 feet of snow melting in the high sierra, he doubted anyone could statistically ingest one cyst.

Pre schools, I am told, also harbor infestations of giardia. And they use treated water.

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Hiking with a Vet on 01/09/2014 18:27:30 MST Print View

"Pre schools, I am told, also harbor infestations of giardia."

They are the vectors and reservoirs for All communicable diseases.

Katy Anderson
(KatyAnderson) - F
Hetch Hetchy chlorination on 01/09/2014 19:07:40 MST Print View

http://www.ridgenet.net/~rockwell/Giardia.pdf

The section in Rockwell's paper (June 2003) where he compares unfiltered Sierra water to San Francisco tap water from Hetch-Hetchy has always bugged me. Let's look at the text:

"Municipal water utilities must use filters to remove the organism. San Francisco city water, coming primarily from the Hetch Hetchy watershed in Yosemite National Park, tested positive for Giardia about 23 percent of the time in 2000, although at very low levels: fewer than 0.12 cysts per liter. This water is of such high quality that the US Environmental Protection Agency and the California Department of Health Services have granted Hetch Hetchy water a filtration exemption, meaning that filtration treatment to ensure its safety from Giardia and other organisms is not required."

It is true that in 2003 there was a filter exemption for Hetch Hetchy. The problem is that from reading this passage one might reasonable infer that the water is delivered to San Francisco taps totally untreated. As Buck so correctly points out, this is not the case, far from it. The water was chlorinated.

Today that chlorination has been replaced by a slightly different chemical treatment and also recently augmented with UV treatment. But that is neither here nor there as Rockwell wrote his paper back in 2003. However not mentioning the Hetch Hetchy water chlorination is a pretty serious omission in my book.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Some responses on 01/09/2014 19:11:12 MST Print View

Tom,

You're welcome. The EPA has said [Giardia]Cysts have been found all months of the year in surface waters from the Arctic to the tropics in even the most pristine of surface waters. Giardia cysts have been found in watersheds where the water looks perfect and where the watershed is classified as "pristine."

David,

Giardia cysts are commonly found in backcountry water sources, so surely people are going to be drinking them on occasion, sometimes in significant concentrations. Also very often, people will scoop water completely free of pathogens. It's not all or nothing, past experience does not guarantee future results for any of us.

Yes, the CDC says that preschoolers often infect others with giardia, and it's because hygiene is lousy. The CDC also says backcountry hikers are in a high risk group if they drink untreated water. It's a very different situation and the CDC has stats to back up both claims.

Greg, I think you have a good point. And I like the sentiment expressed on your avatar.

Katy, Thank you, obviously I agree.

Anyone care to take a stab at refuting other specific points I made about Rockwell's paper?

Edited by Colter on 01/09/2014 21:53:16 MST.

Tom Kirchner
(ouzel) - MLife

Locale: Pacific Northwest/Sierra
Re: Some responses on 01/09/2014 20:29:51 MST Print View

"The EPA has said [Giardia]Cysts have been found all months of the year in surface waters from the Arctic to the tropics in even the most pristine of surface waters. Giardia cysts have been found in watersheds where the water looks perfect and where the watershed is classified as "pristine.""

Aside from this sounding like typical bureaucratic boiler plate, with no quantifying of distribution information, we keep coming back to that word "pristine". Care to give me your definition? IIRC, when you got giardia in the Sierra it presented about 7-8 days after you drank untreated water way down in the Kern Canyon, in an area heavily frequented by horse packers. South of Upper Funston Meadow? That area does not exactly meet my definition of pristine, which is very close to the dictionary definition: "Remaining in a pure state; uncorrupted by civilization" Aside from that, as I mentioned in my previous post, many High Sierra hikers drink untreated water year after year without ill effect. I guess we're all just lucky or asymptomatic?

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Some responses on 01/09/2014 21:07:40 MST Print View

Hi Buck

Your argument is subject to a serious bit of creep.

On the one hand you have:
'Cysts have been found all months of the year in surface waters from the Arctic to the tropics in even the most pristine of surface waters.' (EPA) What this does not specify in any shape or form is how many cysts per litre. It could be 0.01 or less in some cases.

But you changed the meaning in a very serious manner when you followed the above with
'If giardia cysts are commonly found in backcountry water sources'
where I have added the emphasis to the word 'commonly'. There is no way you can get that word out of the EPA statement.

To me, the second statement has such a huge difference from the first that I will cry foul.

Fwiiw, I have had Giardiasis (twice), and my wife and I are very well aware of the risks. We avoid the water in certain areas completely as we know they present a hazard; other areas we get water without treatment.

Cheers

Edited by rcaffin on 01/09/2014 21:10:13 MST.

Buck Nelson
(Colter) - MLife

Locale: Alaska
re: Giardia on 01/09/2014 23:34:33 MST Print View

Tom, I'm afraid you don't recall correctly. It would have been farther north in the Sierra, I was southbound, and the spot I'm thinking of is up high.

As far as the definition of "pristine" I think we both have a pretty good idea of what that means. In GIARDIA: HUMAN HEALTH CRITERIA DOCUMENT, the EPA lists many studies and results from all water types, including pristine sources. I think professionals in the field of waterborne diseases would have a good understanding of "pristine."

Roger, you remind me of my early days on the internet when someone called me a liar because I said a drive to Alaska in March had been cold.

Don't assume I drew my conclusions from a single sentence or source. Here's another EPA quote Giardia cysts are ubiquitous in surface waters of all qualities. (GIARDIA: HUMAN HEALTH CRITERIA DOCUMENT) "Ubiquitous" is a much stronger word than "commonly."

It seems to me like the middle ground is where the truth lies, many people don't get sick drinking untreated water, significant numbers do. Most water has insignificant pathogen levels, some does. Statements like Rockwell's One conclusion of this paper is that you can indeed contract giardiasis on visits to the Sierra Nevada, but it won’t be from the water. are simply unsupported by the facts. That's the kind of thing I'm debating against.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: re: Giardia on 01/10/2014 15:18:21 MST Print View

Hi Buck

I am still crying foul.

> Giardia cysts are ubiquitous in surface waters of all qualities.
But what does ubiquitous mean? It means 'found everywhere', but does not make any statement about quantity.

If every creek and pond has 0.01 cysts per litre, you could legitimately say the cysts are ubiquitous. But you could not say they are 'commonly' found in the creeks or ponds. In fact, it might be more accurate to say they are rarely found, or insignificant.

Cheers

Ben H.
(bzhayes) - F

Locale: So. California
Re: Giardia: Let's Talk SCIENCE on 01/10/2014 16:17:51 MST Print View

Buck, I haven't read through all of the responses (so sorry if you have already covered this). You requested feedback on your conclusions. In you article you state:

"The CDC SPECIFICALLY cited a Welch paper and said Although the advice to universally filter and disinfect backcountry drinking water to prevent disease has been debated (62), the health consequences of ignoring that standard water treatment advice have been documented in WBDOSS [Waterborne Disease and Outbreaks Associated with Drinking Water and Water] In other words, there is documentation, with data, by the Centers for Disease Control and Prevention, that Dr. Welch is wrong."

I consider that pretty serious misrepresentation of what the CDC is saying. They are most definitely not saying that Welch is wrong. They are saying his conclusions are being debated. Additionally, they are saying that IF you get giardia the health consequences are well documented. That is not drawing a conclusion about the effectivity of treating backcountry water.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: re: Giardia on 01/10/2014 18:28:54 MST Print View

Roger, I think "common" is a better synonym for "ubiquitous" than "rarely," but perhaps I'm just being stubborn and argumentative, know what I mean?

Ben, I disagree. the health consequences of ignoring that standard water treatment advice have been documented In that particular statement the CDC is saying they have documentation of the disease consequences of not always treating backcountry water. As a matter of fact, in that statement they don't even mention giardia specifically. They are saying that Welch has debated the issue, not that they are undecided, which is why they cited his article with the "(62)."

Katy Anderson
(KatyAnderson) - F
full sentence on 01/10/2014 21:10:46 MST Print View

This back and forth made me curious enough to go to the CDC article to see what you guys were talking about.

Here is a link to the document: http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5709a4.htm

The quote is from a paragraph titled "Waterborne Disease and Outbreaks Associated with Water Not Intended for Drinking and Water of Unknown Intent" a couple of pages into the text.

The full sentence reads:

"Although the advice to universally filter and disinfect backcountry drinking water to prevent disease has been debated (62), the health consequences of ignoring that standard water treatment advice have been documented in WBDOSS, although they have not been well-defined through research studies."

That last part of the sentence, that Buck left out, changes the meaning considerably.

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: full sentence on 01/10/2014 21:50:04 MST Print View

Katy -
"That last part of the sentence, that Buck left out, changes the meaning considerably."

The full paragraph -
"Backcountry travel (i.e., travel in wilderness environments) in the United States is an increasingly popular activity. In 2004, approximately 12% of Americans aged >16 years (approximately 26 million persons) went backpacking for one or more nights in backcountry areas during the previous 12 months (55). Limited information is available concerning the risk factors for illness in the backcountry and about the health outcomes of visitors who use parks in backcountry areas. Several studies indicate that as many as 3.8%--56% of long-distance hikers and backpackers experience gastrointestinal illness during their time in the backcountry (56--61). Given the increasing popularity of backcountry use, this burden of illness could have significant medical and economic implications. Although the advice to universally filter and disinfect backcountry drinking water to prevent disease has been debated (62), the health consequences of ignoring that standard water treatment advice have been documented in WBDOSS, although they have not been well-defined through research studies. "

What "meaning" changed, and how?

Edited by greg23 on 01/10/2014 22:44:17 MST.

Bill Law
(williamlaw) - M

Locale: SF Bay Area
Re: Re: Nelson's errors in a nutshell on 01/10/2014 22:57:31 MST Print View

A few minutes of Googling is not enough.

A *lifetime* isn't enough :-).

In 2004 they switched from chlorine to chloramine

Sorry; my mistake. I didn't see mention of that little detail anywhere; I now gather that the controversy was due to the fact that chloramine treatment seems to have more side-effects than chlorine.

your point about treatment effectiveness is invalid

Perhaps. While *optimal* chloramine treatment apparently *can* be effective, it isn't obvious that a given treatment with it is. Chloramines are relatively weak disinfectants for virus and protozoa inactivation, per the EPA, for example.

99.9% plus of those cysts would be dead

That isn't obvious to me. First, I still find it incongruous that the cited figures would be for input water. The EPA says in at least one place that it doesn't require measurement of a water system's inflow. And good luck figuring out whether the cited figures are for dead versus viable cysts (it isn't obvious to me how one can even tell one from the other). Regardless, it seems the numbers are pretty useless, regardless, *except* to compare to like numbers (which is what Rockwell did). Maybe the other numbers he cited included dead cysts, also?

a real-world water source which has likely never been tested in history and if it has, likely decades ago

Yet a few lines later you mention a scientist who has done precisely that testing (although I can't find any of his published numbers for Giardia). Rockwell provides citations which seem to contradict your statement. You do a good job of hedging your statement, though; is "likely" 50.1%? is "decades ago" 11 years ago, 16 years ago, or 20 years ago? Does it matter? You could cite Rockwell's paper on that point, but be careful, as we know that paper has at least 4 errors.

Read more here: http://www.modbee.com/2010/05/08/1158938/fouled-waters-sierra-lakes-streams.html#storylink=cpy

I did, including bacterial contamination was easily high enough to sicken hikers with Giardia. I wonder if it could give me the flu, also.

It goes on to say: at high elevations in Yosemite, Sequoia and Kings Canyon national parks, Derlet found a striking difference: Most lakes and streams were clear as champagne and pollution-free.

All in all, the news article you cite (not a technical paper, let alone a peer-reviewed one) is perhaps irrelevant to a discusson of Giaria.

The bottom line: I think to claim Rockwell is in error, one should have to point out the errors in his numbers, or, provide different numbers.

I think I've made this point before: despite your 4 nitpicky complaints with his paper, Dr. Rockwell could certainly have reached the right conclusion anyway. Until I read something that reaches an opposite conclusion and is equally comprehensive and accompanied by as much supporting material, I'm going to continue to drink freely and confidently.

Buck Nelson
(Colter) - MLife

Locale: Alaska
Definitions on 01/11/2014 00:15:35 MST Print View

Katy: "although they have not been well-defined through research studies." What do you think that means? The source link is cited on my blog so people could read the whole thing in context if they liked. I do think the whole statement paragraph clearly supports my statement. The CDC is specifically addressing Welch's claims that there is little or no evidence that drinking untreated backcountry water involves significant risk.

Bill: SF water being run through a modern water treatment plant is not a little detail.

I have talked to the water treatment folks for SF at least three times. The last person cited the water report in saying that the cyst count does not factor viability. So the count, whether at the input or the output, (I have now also heard both,) will end up with a full 3-log plus reduction after treatment.

The fact remains that the actual surface water in the backcountry a hiker is going to drink almost certainly hasn't been tested recently enough (and probably not at all) to be a dependable indicator of pathogen levels.

The bottom line: I think to claim Rockwell is in error, one should have to point out the errors in his numbers, or, provide different numbers. If you don't see any significance in Rockwell's viable giardia numbers for city waters being orders of magnitude lower than he claimed, I beg to differ. And you don't think it's significant that the minimum dose that can sicken someone is not 10 cysts, as Rockwell claims, but one?

"4 nitpicky complaints?" Hardly. They are probably the four most-quoted points of his whole paper, and are the very heart of his arguments.

Edited by Colter on 01/11/2014 10:25:36 MST.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: full sentence on 01/11/2014 14:51:17 MST Print View

> Several studies indicate that as many as 3.8%--56% of long-distance hikers and backpackers
I will stick my neck out and suggest that any survey which produces a result like '3.8% to 56%' is meaningless. You might just as well write 0% to 100% imho.

> bacterial contamination was easily high enough to sicken hikers with Giardia.
Ahhhh... Giardia is protozoa, not bacteria. Any article which confuses the two should probably be used as TP.

There's an awful lot of blathering about this subject, mostly totally incompetant. Compare with the risks of being killed while driving to the trailhead.

Cheers

Edited by rcaffin on 01/11/2014 14:55:21 MST.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: full sentence on 01/11/2014 15:40:58 MST Print View

"I will stick my neck out and suggest that any survey which produces a result like '3.8% to 56%' is meaningless."

Roger, if you go re-read the posting, that is not what was stated. Surveys and studies may be two different things. Also, one is not the same as several. Why do you like to twist the wording around?

For example, one broad study might yield a result as bad as 56%. One narrow study might yield a result of 3.8%. Without knowing the total samples of each study, we don't know how much faith to put in one or the other. That's how they come up with phrases like 3.8% to 56%. That means that there is wide divergence into how bad the problem really is.

--B.G.--

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: Re: re: Giardia on 01/11/2014 16:12:37 MST Print View

Roger said: > Several studies indicate that as many as 3.8%--56% of long-distance hikers and backpackers
I will stick my neck out and suggest that any survey which produces a result like '3.8% to 56%' is meaningless. You might just as well write 0% to 100% imho.


Firstly, they used the word studies (plural) and not survey (singular.) They are referring to not one survey (which might be informal and unscientific,) but multiple scientific studies. [I see Bob beat me to this point.]

Secondly, that quote is from the Centers for Disease Control. In general, people would be well-served if they listened to professional epidemiologists and not the humble opinion of internet people.

Thirdly the CDCs stated range for gastro trouble among hikers is far from meaningless for seemingly obvious reasons. Note their range is "3.8% to 56%" From Wikipedia: The National Outdoor Leadership School (NOLS), which emphasizes strict hand-washing techniques, water disinfection and washing of common cooking utensils in their programs, reports that gastrointestinal illnesses occurred at a rate of only 0.26 per 1000 program days. See the difference?

Roger said: > bacterial contamination was easily high enough to sicken hikers with Giardia.
Ahhhh... Giardia is protozoa, not bacteria.


That of course is a quote from a newspaper article summarizing Derlet's recent research. Just about any newspaper article I read about a topic upon which I am familiar makes some factual errors. Doesn't change what the study actually says though.

From Reducing the impact of summer cattle grazing on water quality in the Sierra Nevada Mountains of California In watersheds where cattle have grazed, 96% of surface water samples contained significant indicator levels of E. coli of 100 CFU/100 ml or more, placing these waters at high risk for harboring the large variety of harmful microorganisms (Derlet et al. 2008). Reducing the impact of summer cattle grazing on water quality in the Sierra Nevada Mountains of California All you have to do is know for sure that cattle haven't recently grazed anywhere in the entire drainage. Not so easy if there's no sign of cattle where you are. I think that's exactly what got me last time.

Roger said: Compare with the risks of being killed while driving to the trailhead. OK, I think drinking untreated water is far less dangerous. Beyond a reasonable doubt however, drinking untreated water has cost me a lot of time and money and discomfort. I do my own risk assessment.

Roger said: There's an awful lot of blathering about this subject, mostly totally incompetant. Pretty poor representation of moderation on the part of someone on the BPL Staff.

Here are a couple of people who are willing to consider other points of view, think carefully, and exchange ideas politely; check out the posts on this thread by William Segraves and KatyAnderson.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Sadism, Necrophilia, and Bestiality on 01/11/2014 17:43:19 MST Print View

" [I see Bob beat me to this point.] "

We're beating a dead horse.

--B.G.--

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Re: full sentence on 01/12/2014 00:05:42 MST Print View

Hi Bob

> For example, one broad study might yield a result as bad as 56%. One narrow study
> might yield a result of 3.8%. Without knowing the total samples of each study, we
> don't know how much faith to put in one or the other.
Happens I actually agree with you.

The survey in this case was that by the CDC which produced these figures from a number of studies. But with such a wide range of results one has to conclude that none of them are reliable. Alternately, depending on one's point of view (or vested interest), with those results one can claim any value one wants. You want a real low value? Try this paper. You want a real high value? Try that paper.

In short, the results are meaningless, except that they show that one can get Giardiasis from the mountains.

Now, am I implying that either Bob or Buck is incompetent? Nope. Never said that.

Am I suggesting that the newspaper report was incompetent? Too right. The problem with quoting such a 'report' is that if left unchallenged it becomes part of the folklore. So I pointed out that it was illogical.

Cheers

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: re: Giardia on 01/12/2014 00:23:35 MST Print View

Hi Buck

First, see above reply to Bob.

> Roger said: There's an awful lot of blathering about this subject, mostly totally
> incompetant. Pretty poor representation of moderation on the part of someone on
> the BPL Staff.
First of all, not every posting of mine is 'moderation' (either as 'mild' or as 'moderator'). I am entitled to my opinion, just the same as everyone else. And sometimes I am a bit too concise.

Second, I stand by my comment about blathering, but perhaps I need to clarify that I was referring to things like the newspaper article. Any reporter who confuses bacteria and protozoa is clearly way out of his depth, and is blathering. I was not referring to either you or Bob. Sorry if you thought otherwise.

I note the interesting figure you quote from NOLS of '0.26 per 1000 program days'. Seems to me that is a lot less than 3.8%, however you define the conditions. That said, I think it brings a lot of the debate back into perspective, and that data is probably more reliable then many so-called research papers with relatively tiny study populations or uncontrolled self-reporting.

However, bear in mind that the NOLS data does not mean the 0.26/1000days figure must come from water supplies. It could equally come from a few cases where kids did not wash properly. That NOLS get such good results by being aggressive with the demands on hand washng does imply that without that aggression the figures would be far worse - which says something about the NOLS participants. Interesting data, but no controls for comparison.

> In watersheds where cattle have grazed, 96% of surface water samples contained
> significant indicator levels of E. coli of 100 CFU/100 ml or more,
Now that is a useful bit of information for everyone, but hardly unexpected. Me, I would round the figure up to 100% just to be safe! Thank you for that.

Cheers

Jennifer Mitol
(Jenmitol) - M

Locale: In my dreams....
Re: Sadism, Necrophilia, and Bestiality on 01/12/2014 07:50:38 MST Print View

Well Buck, I appreciate your beating this dead horse. And despite my temptations on numerous occasions to drink that "pristine" water, I have taken your advice and treat no matter what.

Besides, after watching all those trains of pack animals trudge through those "pristine" streams and defecate right next to the lakes along the JMT...I would never drink from that water without treatment.

And I do wish people would stop substituting personal anecdotal experience for scientific studies. Just because YOU haven't gotten giardia from 20 years of drinking untreated water doesn't mean it's not in the water.

We used to think bleeding people helped them overcome illness because WE SAW IT! They had a fever, we put leeches on them, they got better...Of course!!!!!

William Segraves
(sbill9000) - F - M
Re: Re: Re: Re: re: Giardia on 01/12/2014 09:27:54 MST Print View

"I note the interesting figure you quote from NOLS of '0.26 per 1000 program days'. Seems to me that is a lot less than 3.8%, however you define the conditions. That said, I think it brings a lot of the debate back into perspective, and that data is probably more reliable then many so-called research papers with relatively tiny study populations or uncontrolled self-reporting."

NOLs purifies their water. It's the comparable frequencies for those who *don't* purify the water that we'd most like to know about, right?

Bill S.

Katy Anderson
(KatyAnderson) - F
not well-defined on 01/12/2014 12:50:06 MST Print View

Greg says:
What "meaning" changed, and how?

Buck says:
What do you think that means?

Sorry, I must have been unclear in my original post. I will try again.

The part of the sentence that Buck quotes in his blog post is:
"Although the advice to universally filter and disinfect backcountry drinking water to prevent disease has been debated, the health consequences of ignoring that standard water treatment advice have been documented"

Reading this I infer that drinking untreated water has bad health consequences and the CDC has the data to back that statement up.

The part of the sentence that Buck left out is:
although they have not been well-defined through research studies."

This for me puts the first part of the sentence in a totally different light. Why?
Because as I read it the CDC is saying that the health consequences of drinking untreated water was not well-defined through research studies.

Which puts us all back at square one.
Question: What happens if you drink untreated water?
Answer: Not well-defined through research studies.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: not well-defined on 01/12/2014 13:37:55 MST Print View

Other half of the equation is what's the cost of treating

$20 and 2 ounces for Squeeze Mini. Minor hassle.

or other treatment methods

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Re: Re: re: Giardia on 01/12/2014 13:52:12 MST Print View

William wrote:

> > interesting figure you quote from NOLS of '0.26 per 1000 program days'.
> NOLs purifies their water.

Hum - interesting. IF NOLS treats their water with something meeting EPA Standards, then where did the 0.26/1000 get their infection? I don't know.

Cheers

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Re: not well-defined on 01/12/2014 13:53:22 MST Print View

Katy -

"This for me puts the first part of the sentence in a totally different light. Why?
Because as I read it the CDC is saying that the health consequences of drinking untreated water was not well-defined through research studies.

"Which puts us all back at square one.
Question: What happens if you drink untreated water?
Answer: Not well-defined through research studies."


So even though consequences have been documented, you will wait for "well-defined studies" before deciding to treat your water?

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: Re: Re: Re: re: Giardia on 01/12/2014 13:58:14 MST Print View

"IF NOLS treats their water with something meeting EPA Standards, then where did the 0.26/1000 get their infection?"

I've seen lots of beginner backpackers who start with a proper filter, but their use technique is lousy. I've seen beginners rinse out cookware with raw water, and then use it immediately.

--B.G.--

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Re: Re: Re: Re: Re: re: Giardia on 01/12/2014 14:03:02 MST Print View

Roger -
"Hum - interesting. IF NOLS treats their water with something meeting EPA Standards, then where did the 0.26/1000 [program days] get their infection? I don't know."

Poor personal hygiene, spread through sharing food, or food prep, would be my guess.

Even though NOALS goes to great lengths stressing proper toilet activities, it would not surprise me if someone out of a group of 20, over the course of 30 days in the field, times 70 trips, didn't get it exactly right.

Edit 1: And IIR, one case study (not NOALS) traced GI problems to soapy cookware as a result of poor rinsing. So, not all GI episodes are microbe related.

Edit 2: I personally observed a NOAL dinner where "fresh/frozen" chicken was being prepped for inclusion into burritos. I didn't see a lot of hand washing or utensil segregation during that process, and Hoped that things were being well cooked. They did taste great!

Edited by greg23 on 01/12/2014 14:31:17 MST.

Buck Nelson
(Colter) - MLife

Locale: Alaska
re: Giardia: Let's Talk SCIENCE on 01/12/2014 22:40:21 MST Print View

Jennifer: Thanks for that. I think it's worthwhile and I actually think we've covered lots of new ground on this thread along with the standard debating points.

Bill said: NOLs purifies their water. It's the comparable frequencies for those who *don't* purify the water that we'd most like to know about, right?" That's true. There's not a good matched control group, but I think the results of their handling of water, hands and cookware vs the general public is meaningful.

"Medical risks of wilderness hiking" which may or many not have been mentioned on this thread, did a study on a large group of backpackers and found, like NOLS: Diarrhea is the most common illness limiting long-distance hikers. Hikers should purify water routinely, avoiding using untreated surface water. The risk of gastrointestinal illness can also be reduced by maintaining personal hygiene practices and cleaning cookware. http://www.ncbi.nlm.nih.gov/pubmed/12681456

Katy Anderson: I think they are clearly saying there is documentation of consequences for drinking untreated backcountry water. As you know we've discussed scientific papers containing some of that documentation on this thread. I THINK the CDC is saying there are gray areas (not well-defined by studies,)like the attack rates, risk factors, relative importance vs. hygiene, etc. Anyone know the definition of "well-defined" in this context?

Bob and Greg, Good points.

Edited by Colter on 01/12/2014 22:41:07 MST.

Jennifer Mitol
(Jenmitol) - M

Locale: In my dreams....
Re: re: Giardia: Let's Talk SCIENCE on 01/15/2014 09:17:08 MST Print View

Whenever you look at review papers, or meta-analyses, they usually couch their findings with some sort of "need more research" statement. It is exceedingly rare to get a full on recommendation about anything medical at this point, as we are all well-aware of the limitations of the scientific literature.

HOWEVER...we do know a little. It may not be perfect, it may not be conclusive, but the literature that is out there certainly suggests that it is quite possible to be infected with giardia from untreated surface water in the backcountry. So until we have more studies that tell us otherwise, why in the world would you risk it? The cost-benefit ratio just doesn't seem to at all favor taking the risk.

Seatbelts? The likelihood of my getting into an accident is low, but I'm going to wear it anyway because the risk exists and I know a seatbelt will minimize the damage. Same with helmets.

I guess I just don't see why people are so rabidly anti-treating and feel the need to spread that word. If you want to take the non-treatment risk and drink horse poo, then go for it. But at least do it honestly.....

Charley White
(charleywhite) - F

Locale: Petaluma, CA
A non-scientific reason on 01/15/2014 12:46:27 MST Print View

[major re-write to remove scientific assertions disguised as opinions]

Jennifer Mitol wrote: " So until we have more studies that tell us otherwise, why in the world would you risk it?"

In my case the answer is emotional: pure unadulterated joy. Rockwell's piece sent me back to my youth when I first fell in love with moving through nature, watching, learning, observing, sensing, and participating directly. Getting back into camping as an adult, suddenly there was a new bug and almost all of my college educated brainpower went into evaluating that. The joy I felt, unleashed by Rockwell, bending over to drink freely from a mossy springlet so presenting with the signs I'd learned how to identify clean water in the wild, is inexpressible. The joy of being a member and not engineer of nature.

But I feel I can say that from a position of informed, if not decimal-self-quantified, risk avoidance. I've read literature without reviewing as a peer. I merely believe/suspect that PPM and not single-cyst is material. Identifying bias and re-interpreting seems half the battle in learning from objective studies themselves.

Edited by charleywhite on 01/15/2014 13:40:12 MST.

Ben H.
(bzhayes) - F

Locale: So. California
Re: Re: re: Giardia: Let's Talk SCIENCE on 01/15/2014 14:40:01 MST Print View

"I guess I just don't see why people are so rabidly anti-treating and feel the need to spread that word. If you want to take the non-treatment risk and drink horse poo, then go for it. But at least do it honestly....."

First let me say, I treat all of the water I consume. I think the anti-treatment group is a backlash to fear mongering on the treat water side. People are seriously afraid of consuming water which is probably completely safe to drink. Thank can have real consequences. People could face serious dehydration and even death due to out of proportional fear of drinking untreated water.

I am all for getting the facts straight. I think people should evaluate the risks for themselves based on sound scientific research. I was really interested in this topic, but I think the OP got off topic right from the get go in trying to promote a specific conclusion. I think the science is up in the air as to whether it is necessary to treat certain backcountry water. We should be promoting what the science says, not spend all of our time telling people what to do.

Larry De La Briandais
(Hitech) - F

Locale: SF Bay Area
To filter or not to filter, is that the question... on 01/15/2014 15:15:54 MST Print View

There is a clear mountain stream in the Sierras that for many, many years we drank from without treating. No one had any problems (though I believe that I am "immune" to giardia). Then one of us got a filter and the water tasted better to me (no silt). So, I got a filter too, can't be left behind in the gear arms race! ;^) Now, I filter all the time, but I wouldn't hesitate to drink from that stream if I couldn't filter.

It comes down to it being so simple to filter that I do. The sawyer filters make this quick, easy and light. And one never knows when something can change. And, I don't have to evaluate each water source I come across. I don't have to pass up a questionable water source looking for a better one.

That said, way too big a deal is made about the dangers of drinking untreated water. The day hikers I rescued at Nevada Falls in Yosemite would have been way better off drink untreated water. Any problems would have occurred once they were safely home, instead of nearly passing out from heat exhaustion brought on by sever dehydration.

Edited by Hitech on 01/15/2014 17:41:28 MST.

Justin Baker
(justin_baker) - F

Locale: Santa Rosa, CA
studies, papers, whatever... on 01/15/2014 15:22:29 MST Print View

I really don't care what some study or peer reviewed paper has to say.
The truth is that my father and his father went on many backpacking trips where they didn't treat water. At the time nobody was treating water. They never got sick and nobody they knew ever got sick. I have met hikers who are twice or three times my age who have never treated and never gotten sick. Mountain water sources are the same as they were 50 years ago. This is why I don't treat much of my water.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: studies, papers, whatever... on 01/15/2014 17:25:26 MST Print View

> Mountain water sources are the same as they were 50 years ago.
Extremely unlikely.
I suggest the number of uncivilised novices pooping near creeks and lakes, and the amount of cattle intrusion, have both increased.

Cheers

Justin Baker
(justin_baker) - F

Locale: Santa Rosa, CA
Re: Re: studies, papers, whatever... on 01/15/2014 18:31:24 MST Print View

You are probably right about that Roger, but I was thinking more about water sources that are away from well beaten trails or off trail all together. I always treat water along trails that allow stock travel, no exception.

I do a lot of hiking in Big Sur and there is this place called Sykes Hot Springs that attracts 90% of the hikers in the area. After I heard a story about some old dirty hippie pooping directly into the big sur river (apparently he said something like "mother nature will clean me up man!") I always treat downstream from Sykes. But any of the side streams and creeks leading into the river are fair game for me.

To my knowledge, cattle intrusion has actually decreased in US wilderness areas over the past few decades (someone correct me if I'm wrong on that). There was a time when sheep herds ran around the high sierras decimating pristine meadows.

Edited by justin_baker on 01/15/2014 18:38:21 MST.

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Re: Re: studies, papers, whatever... on 01/15/2014 18:44:02 MST Print View

"Although humans are the main reservoir of the parasite, a variety of domestic and wild animals, such as dogs, cats, cattle, beavers and deer carry Giardia species and can infect humans."

YMMV

Buck Nelson
(Colter) - MLife

Locale: Alaska
Giardia: The truth is the middle ground on 01/15/2014 21:05:14 MST Print View

I understand the appeal of drinking straight from the source. I've done it myself.

Facts and personal risk assessment are two separate but related issues.

In my OP I cited one of Dr. Welch's papers. (Almost all roads in the "giardia myth" science lead back to Rockwell, Welch and Derlet, with Derlet being by far the most scientific.) There is no evidence that wilderness waters in the United States...are unsafe for consumption. Thomas R. Welch, MD. (Source: Adirondack Explorer, May/June 2009.) I am not trying to impose choices, but I am arguing against demonstrably false statements like Welch's because they are the "facts" upon which many people base their choices.

Public health agencies are unanimous on the topic, or nearly so: there is significant risk in drinking untreated backcountry water, although the exact degree of risk is clearly unknown.

Treating is a personal choice. No one should allow themselves to become severely dehydrated if they run out of water and any reasonable looking source is available.

After researching the facts at length, my personal choice is to treat nearly all surface water. Others may do as they wish.

That said, I stand by the facts I've presented until proven wrong by documented evidence to the contrary.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Giardia: The truth is the middle ground on 01/15/2014 23:20:45 MST Print View

"my personal choice is to treat nearly all surface water"

Exactly. I treat nearly all water. The possible exception is if I can see water dripping off a snow bank and I can't see the paw tracks of grubby little mammals.

--B.G.--