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Giardia: Let's Talk SCIENCE
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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?



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

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?


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.

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.

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. 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

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

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:!;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.