Forum Index » General Lightweight Backpacking Discussion » Giardia: Let's Talk SCIENCE


Display Avatars Sort By:
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.