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Why Rockwell is Wrong about Giardia

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Re: Why Rockwell is Wrong about Giardia

Postby SweetSierra » Sat Feb 23, 2013 5:42 pm

I haven't read all the posts in this thread. I'm assuming you're discussing a study that came out over 10 years ago. I believe it said that giardia was not as great a threat as has been advertised and that the cases of people becoming ill may be due to other factors (lack of proper hygiene). Forgive me if you're discussing another study.

I read articles on the study at the time and my husband and I decided to stop treating Sierra water. Each year we did 9-10 day trips in July, August, and September and more than one trip a year. My ex-husband hikes almost every other weekend in the summer and is out sometimes for two months total. He hasn't yet had a problem. The water sources range from creeks, rivers, and lakes, some fairly heavily used, some more pristine. I haven't had any serious problems, ones I would relate to water and I haven't contracted giardia. I make sure the water I take isn't from a stagnant pool. I have pushed my luck at drinking water from some lakes that are heavily used. From my experience as a human lab rat, I would say that it isn't as much of a problem as was once thought, though I would still be careful about what I use as a source of water. Just my opinion :)
Last edited by SweetSierra on Mon Feb 25, 2013 8:28 am, edited 2 times in total.



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Re: Why Rockwell is Wrong about Giardia

Postby mokelumnekid » Sun Feb 24, 2013 10:16 pm

There is a lot about this that increasingly gets under my skin. As someone who has had a career in "science" in the less-than-well-behaved natural work (25 years academic geology/geophysics) I smelled trouble from the title of this post, "WHY..." when I haven't yet seen any thing that clearly tells me WHY this is WRONG. Incomplete, obviously. Subject to a large number of caveats, of course. But in my reading of Rockwell there was never an intent to deceive. Are more studies needed? Of course. Is there any prospect of a truly definitive study that clearly rationalizes all the degrees of freedom and their seasonal and decadal change? Likely not.

So instead of yammering on about "science" dear Colter, please outline for us, subject to the kinds of constraints all of us working scientists have in terms of funding and man power, the details of a study that is: doable in a three year time frame, covers the variability in a mountain range that is hundreds of miles in length with numerous microclimates, is definitive in terms of biological sources and sinks, and leads to some conclusions that are better in terms of "science" than the anecdotal experiences that people now share. Pray tell what is the "science" you seek with a clear work plan, milestones, testable hypothesis, funding plan that somehow is say, an order of magnitude improvement in understand the risks from a quantitative basis, and who would fund this work? These are minimum requirements for working scientists, and so I would expect you to be fully invested in understanding the likelihood of significant progress in light of these constraints in your braying for "more science."

I suppose we could take the view that refuting Rockwell's conclusions with one negative test, or by revealing that his primary, secondary or tertiary assumptions are not generally sound, would suggest that all his conclusions are wrong. But given the small sample sizes in all aspects of the realm of applications it is neither possible to convincingly refute or support the essence of his conclusions. Do people suffer from giardia? Seems so. Do many others not suffer? That is true as well. Both are allowed by his study.

So, to close, what IS the science you speak of that will quantitatively do an order of magnitude more than the end-members of "**** happens" and the Boy Scout motto of "Be Prepared"? Convince me that the nature of this science will fully illuminate and refine our understanding of risk of giardia.
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Re: Why Rockwell is Wrong about Giardia

Postby Colter » Mon Feb 25, 2013 12:34 am

mokelumnekid

People can think rationally, do their own research and draw reasonable conclusions without three year time frames and funding plans.

You failed to respond to a single point I made in my original post. People have made decisions to not treat/filter based on each of those major points Rockwell made that I addressed. If you can refute each of my points in that post I'll be impressed, but I'm confident you can't.

I've gotten emails from several PHDs with degrees in related fields, like microbiology, who agree with these points I've made, so arguments addressing the usual workings of academia are not going to do anything to change my conclusions. I will listen to reasoned arguments however.

If I responded in kind to your personal insults I suppose the thread would be locked, so I won't.

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Re: Why Rockwell is Wrong about Giardia

Postby mokelumnekid » Mon Feb 25, 2013 12:04 pm

So show me *your* research that you refer to that illuminates the questions with either new data or a scholarly assessment of the field. That was the point of my post. Scientific protocols are that it isn't enough to simply try to pick apart someone work, but instead make an advancement based on new constraints that are widely viewed as having more power of explanation.

If the thread was just about Rockwell I wouldn't have bothered to respond. But you have repeatedly made statements that somehow missing "science" will set everything straight. I was curious about whether you understand what that meant from a practical standpoint, and what you would consider a study of sufficient scope and complexity to be an advance.

So instead of harping on Rockwell, it would be much more interesting, informative and useful if you were to share with us your vision for how one can get to the bottom of this question. Just help us understand how one should decide to either: filter all the time, sometimes filter, or not at all. I am not a microbiologist and I don't understand the field well enough to craft a robust research proposal myself.
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Re: Why Rockwell is Wrong about Giardia

Postby Colter » Mon Feb 25, 2013 12:57 pm

mokelumnekid wrote:So show me *your* research that you refer to that illuminates the questions with either new data or a scholarly assessment of the field.

Please see the original post where I assessed key elements of his paper. I will discuss that. I'm not going to debate against your emotion.

I did my graduate research on Giardia and Cryptosporidium 10 years ago...I found Giardia and cryptosporidium in every stream I tested, including streams in protected watersheds (pristine forests that the public is not allowed in to protect water quality)...I have found it [Rockwell] to be poorly researched, poorly referenced, and contained many glaring errors. I started reading this and I wondered how a pHD could publish such a piece of crap, then I read his bio. What was published was one layman's opinions on the internet [that] would not have stood up to peer review. The author of the paper is actually doing a huge diservice to the community by publishing information that is just plain wrong...He presents an opinion piece (can't even be considered a balanced literature review) in the guise of a research paper. People read this and incorrectly believe they can't catch Giardia from drinking out of streams in the backcountry.

http://cascadeclimbers.com/forum/ubbthr ... s/197894/1
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Re: Why Rockwell is Wrong about Giardia

Postby chrisdiercks » Mon Feb 25, 2013 1:09 pm

Boy Colter, where do I start. I guess the OP. So off we go......

Years ago I had Giardia two or three times (twice diagnosed, once lab tested) and became a true believer in water treatment. Before hiking the PCT I reread Rockwell's Giardia lamblia and Giardiasis With Particular Attention to the Sierra Nevada It cited dozens of scientific papers and had this as a leading quote: Neither health department surveillance nor the medical literature supports the widely held perception that giardiasis is a significant risk to backpackers in the United States.

Despite my experience to the contrary, I was convinced, and followed his advice of choosing my water sources. In few weeks I had my first case of giardia in over 20 years.


This is kind of a side line (in a way), but dude, why did you ignore your own experience? Lets just look at the shark attack analogy at a different angle for a second. If I want to surf Ano Neuvo State Park or Waddell Creek, (both known great white feeding areas) I can minimize the risk to a certain extent but NEVER completely get rid of it. Giardia? If I had been in your situation,I would just treat the water; a slam dunk with proper hygiene. Seriously, who with any common sense would question your choice to treat.

Since that time I've spent weeks of research and have found that the medical literature overwhelmingly refutes his main conclusions.


The overwhelmingly refuting Rockwell's main conclusions thing? No. Strongly suggesting that additional work needs to be done; a resounding yes!

For example, Rockwell says that Sierra water is cleaner than San Francisco city water. Absolutely false. San Francisco water is run through a water treatment plant.


Clearly, you have no idea how water plant treatment permitting works. You cannot say absolutely false to Rockwell's statement. Data does not and will not back that statement up. I would be more skeptical of our water treatment facilities if I were you.

His calculations on how many liters of water one would have to drink to get giardia in the Sierras are worse than useless. For one he uses water tests decades old. And he uses 10 cysts as the "infective dose." You will actually find the "10 cysts" repeated many places on the internet, but again, it's untrue. Experts have determined that there is a 2% chance of being infected by a single cyst. http://www.waterbornepathogens.org/inde ... &Itemid=38 The FDA says Ingestion of one or more cysts may cause disease


Ok...I am trying to explain as nice as possible how you have no idea what you are talking about. Your conclusions are totally erroneous. It seems that you completely fail to grasp what these guys are saying when describing their data sets and conclusions. I can't explain it to you because you do not seem to even understand the concept of a probability distribution function (pdf). Some of these results were generated (that means generated using computers and theoretical mathematical models) using Monte Carlo simulations and you are going to tell me you understood that? I've done modeling and presented to regulators...it's not the most comfortable position to be in...always because the lack of data to completely validate and verify the model. I could babble a whole lot more, but I seriously doubt you are going to get it. Nuff said.

I was able to find only two studies that tested hikers BEFORE and AFTER a trip to the field. They showed a minimum of 5.7% of hikers contracted Giardia in a single trip. Seems high, but it does show the risk can be very high at times. http://www.ncbi.nlm.nih.gov/pubmed/937629


Interesting stuff. Suggests more study needed. Note that the study was not in the Sierra Nevada and apparently that way too many variables are flopping in the wind to really nail stuff down. The actual study would be much better than the abstract to look at. What is really needed is stuff like where these groups went and who got sick; you know, detailed trip itineraries. This study generally supports your idea that the threat of giardia is under reported, but slam dunk proof it is not.

Are hikers getting giardia because of poor hand hygiene? Maybe. But when backpacking most of us are interacting with very few people compared to our day-to-day lives, and the only study done on hiker fecal hand contamination actually found hiker's hands were dirtier when they STARTED their hikes. http://www.adirondoc.com/publications/h ... n_2012.pdf


When I saw this, I thought "here we go, something interesting". But it ended up a classic example of why I'm saying you do not understand what is going on with the data. Your conclusion is false. Seriously, this is not even close to being a discussion point. When asked the question, "can you distinguish between the two populations of data using the Wilcoxon signed-rank test at 95% Cl", my high school aged daughter answered correctly at NO. To be fair, she has taken a college level stats class. But this is a classic entry level statistics class question and you got it wrong. Did the guys writing the article get it wrong? I'll quote from the article;

"Comparison of mean hand f-CFUs was similar, and the Wilcoxon signed-rank test showed no difference in hand colonization before and after trip, P = .27."

I'll interpret for you; they said that you cannot tell the difference and got the question correct. So, apparently not only do you not understand statistics, you also do not seem to read (or understand?) most of the paper these guys presented. Note that they also concluded the following;

"Our study adds to a growing body of evidence that supports suboptimal hand hygiene among backpackers."

:soapbox: If you can't understand the statistics at this elementary level, how are you going to understand the ramifications of a Monte Carlo analysis? I can barely discuss it myself right now I'm so out of the loop and I used to understand all the assumptions and theory. If any of your PhD contacts were to back you on this (not the Monte Carlo) particular analysis, they should be publicly humiliated. To have a valid scientific evaluation means you have to use science correctly, and statistics is a part of that science.

Rockwell says “If you get a Giardia infection, you are unlikely to have symptoms.” Maybe, but a Colorado survey (cited just above) of 256 infected people showed they were sick an average of 3.8 weeks and lost an average of about 12 pounds. Several backpackers appear weekly at Centinela Mammoth Hospital in Mammoth Lakes sick enough with giardiasis to need urgent care, said Dr. Jack Bertman, an emergency physician... [quoted from the LA Times.]


Interesting stuff here. Again, the Colorado survey...different population, climate, ect., but it does suggest further work is needed to nail down what is going on. I found the 1988 LA Times article quoting Dr. Bertman, but there is no documentation again suggesting more work necessary.

I would enjoy hearing your comments!


This is also apparently not true. For instance, you seem to have taken mokelumnekid's comments as personal insults and they were not. They were all just comments. All of my above comments are NOT A PERSONNEL ATTACK on you. You asked for me to respond to your OP and I have done so honestly and earnestly. These appear to be harsh criticisms, but they are also valid. You want my advice? Take an intro level statistics class at a local community college. You could probably do it on line. It will give you a whole new perspective on data. Basically, I think the largest problem is that you are out of your depth. When calling my previous comments deep in rhetoric I laughed my ass off. Granted, the comments were heavily peppered with jargon and for that I apologize; not rhetoric though. But basically you really have no idea what I was talking about do you, and you could have just asked.

As for the Rockwell article? I'd forgotten what was in it so it was good I read it again. I think mokelumnekid sums it up fine with;

I suppose we could take the view that refuting Rockwell's conclusions with one negative test, or by revealing that his primary, secondary or tertiary assumptions are not generally sound, would suggest that all his conclusions are wrong. But given the small sample sizes in all aspects of the realm of applications it is neither possible to convincingly refute or support the essence of his conclusions. Do people suffer from giardia? Seems so. Do many others not suffer? That is true as well. Both are allowed by his study.


Actually, I'm more negative toward it, but I can't really argue with those conclusions. And the guy peppers his article with plenty of CYA (cover your ass) statements. Do I think giardia is an issue in the Sierra? Yup. Do I think more study needs to be conducted in the Sierra? You betcha!


I was hoping you had additional data/sampling studies from the Sierra. But alas, apparently not to be. The optimist in me is hoping you can learn from this. You need to be able to admit when you don't know something. I've spent 5 hours, on just 1 page of an article, just trying to understand how they arrived at those conclusions; Just to master all the assumptions involved, all the strengths and weaknesses of their argument or derivation. It was an ugly and painful process for me, but I learned a whole lot by doing it. Take that stats class and/or volunteer to help out with a local sampling program of some kind. You'd be surprised how that will change your appreciation of what data is and how to handle it.

Gentlemen and gentlewomen, I am out of this discussion!

Chris
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Re: Why Rockwell is Wrong about Giardia

Postby Colter » Mon Feb 25, 2013 2:15 pm

Seriously, who with any common sense would question your choice to treat. Rockwell.

I originally believed the Rockwell paper because correlation is not causation. I was convinced that my experience was a fluke and the science showed it was unlikely to happen again. But Rockwell was wrong. I should have done my own research beforehand.

You cannot say absolutely false to Rockwell's statement. [that Sierra water is cleaner than San Francisco water] I can say that and I do. Tested levels for raw water are roughly at the same level. Then SF water is treated with UV which kills something like 99.9% of giardia. Plus the chlorine and chloramine. SF water is at least 1,000 times safer from giardia.

Despite your condescending response to my point about the infective dose being lower than 10 cysts, it's true. This is from professionals in the field: The theoretical infectious dose for Giardia is ingestion of a single infectious cyst...The probability of infection has since been described (Rose et al. 1991) by two exponential models:
Psingle = 1 – exp(–rN) and Pannual = 1 – (1 – Psingle)EF

http://www.waterbornepathogens.org >giardia > infective dose

Even without those calculations a critical thinker can look at the original Rendtorff charts and see that the infectious does is going to be less than ten cysts which invalidates all of Rockwell's calculations on the amount of water needed to achieve an infective dose and hence, his risk assessment.

In the Zell study in the Sierra 5.7%+ got giardia in a single trip. http://download.journals.elsevierhealth ... 711729.pdf

Here's what the backpacker hand contamination study showed: The prevalence of fecal hand contamination in entering and exiting hikers was similar (33% and 27%, respectively) Your numerous paragraphs laced with condescending rhetoric don't change that.

you seem to have taken mokelumnekid's comments as personal insults and they were not. "Braying" and "yammering" strike me as insults.
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Re: Why Rockwell is Wrong about Giardia

Postby gdurkee » Mon Feb 25, 2013 9:06 pm

OK. I lied, I got sucked into this again (somehow I wasn't getting update notifications, so didn't realize this was still going). I am a weak, weak person.

This statement has been bothering me.

vs a Sierra physician's experience

Several backpackers appear weekly at Centinela Mammoth Hospital in Mammoth Lakes sick enough with giardiasis to need urgent care


Like Rogue, it just doesn't agree with my experience. Through the wonders of Google, I found the origin. It's from a 1988 LA Times article on giardia (http://articles.latimes.com/1988-07-26/ ... re-program)

That doesn't necessarily make it wrong, but it's not exactly timely. My memory from giardia diagnosis in those days (and a friend of mine was very susceptible) was that many doctors were treating on symptoms, because stool samples were not that reliable and many people didn't tolerate the string down the throat to catch a few giardia critters. As such, the estimate of cases may be higher than were actually giardia.

And if Eric would just add a Like button, I'd give one to mokelumnekid for his very detailed explanation of interpreting and understanding statistics. That plays a huge and overlooked part here -- almost to the point of willful ignorance. And it leads to the real question of what's the point? OK, Rockwell was not spot-on. His report,though, got a lot of people out of what was approaching hysteria about water safety in the Sierra. He's not a pathologist or an MD and just got interested. Excellent amateur effort, I still say. All science is eternally subject to revision. Nothing cited here has caused me to rethink or revise the advise I give zillions of times to hikers: If you have something to treat the water with, do so. If it breaks or you run out of chemicals, drink water anyway. If you want the singular experience of drinking pure Sierra water and are reasonably careful, the odds are well in your favor.

California had about 1800 cases in 2009 & 2010 with a rate of about 5 cases per 100,000 people. So let's maintain some perspective here (unless, of course, you're one of those cases...). No idea how many are from drinking water on recreational trips, but I'd be really interested in knowing. Once again, though, my experience is there's just darned few.

Good reference: http://www.cdc.gov/mmwr/preview/mmwrhtml/ss6105a2.htm

g.
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Re: Why Rockwell is Wrong about Giardia

Postby mokelumnekid » Mon Feb 25, 2013 9:30 pm

"Braying" was unfortunate and I apologize for that remark. "Yammering" not so much. I'm still trying to figure out if you really know what you are talking about from the stand point of a deeply considered approach, an understanding of the scientific method and the practical requirements in making a scientific advance in this question. Or are you simply repeating scraps you have gathered from other online threads, with no more peer review than Rockwell's? Are you going to advance the question (good!) or simply cut-and-paste stuff you have read online elsewhere?

So to the point of my second post which you disregard: please outline for me what you consider to be a study that is sufficiently comprehensive such that the issue can be put to rest, or at least advanced. You quote work, also very fragmentary, that would suggest that we are swimming in Giardia. (BTW I have no dog in this issue- I thought Rockwell's amateur assessment to be an important opening in what would hopefully become a widely researched topic.)

So, please and finally, detail for us a useful study that is:

1) Doable with the usual logistical constraints that any agency scientist has,

2) Would provide both broad and local insights as to the likely causes and seasonal distribution of Giardia as a function of latitude (Tahoe area, Ebbetts to Sonora, YNP to Piute drainage, Piute through SEKI and so on).

3) Would identify likely sources for the Giardia: cows, people, marmots, sheep, horses, sea gulls, fish, meteors, ???

4) Gather all this into a risk-based assessment

What I'm driving at here is what do YOU consider to be a sufficiently robust science-based study that would advance the questions past you simply rehashing others on-line postings against Rockwell's? I'm not defending Rockwell, just that I'm curious as to what you would consider to be the bare bones of a science based study that would illuminate the issue and how might one do that in the real world?
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Re: Why Rockwell is Wrong about Giardia

Postby mokelumnekid » Mon Feb 25, 2013 9:55 pm

I just read the article in Wilderness medicine that Colter cites and if anything it is as ambiguous as Rockwell's. Good grief. Most of those folks in that (too small sample set) filtered and the author's more-or-less threw up their hands at ascribing the symptoms to Giardia

To quote, "None of the affected participants had G. lamblia infection noted in their stool specimens."

Read it for yourself folks:

http://tinyurl.com/bdyt2v4

Yeah, I'm done with this thread too....
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Re: Why Rockwell is Wrong about Giardia

Postby Colter » Mon Feb 25, 2013 11:22 pm

mokelumnekid,

I am not simply "cutting and pasting" what other people have written. I researched out the infective dose issue. I discovered Rockwell's insinuation that San Francisco was using raw water wasn't true. I researched the kind of filters used back then to test water for giardia and found out that only about 10-30% of cysts were recovered. I learned "pulse contamination" isn't factored in and can wildly skew the results of testing. I researched whether Rendtorff had verified his giardia cysts were viable. He hadn't. So get off your high horse.

Here's a couple of blog posts I've written. My own words, with citations of peer-reviewed papers.
Backpacker Giardia: Debunking a Skeptical Paper
http://bucktrack.blogspot.com/2012/09/b ... cal_8.html
Waterborne Giardia for Backpackers: No Myth
http://bucktrack.blogspot.com/2011/03/w ... rs-no.html

are you simply repeating scraps you have gathered from other online threads, with no more peer review than Rockwell's? If you read what I've already written on this thread and thought for an instant you'd know your question was B.S.

Ask any statistician/epidemiologist familiar with giardia and ask them if Rockwell's stats are legit and support his claim "...you can indeed contract giardiasis on visits to the high mountains of the Sierra Nevada, but it almost certainly won’t be from the water. So drink freely and confidently." I'll bet you can't find ONE that agrees with that, and I'm certain the majority would disagree.

So, to close, what IS the science you speak of that will quantitatively do an order of magnitude more...
As far as I know that's just a pure straw-man argument. A study like that would be difficult. In the meantime, we need to avoid disinformation like Rockwell's. The Rockwell paper, often considered the gold standard, is, in the words of the giardia expert quoted above poorly researched, poorly referenced, and [with] many glaring errors. I independently came to the same conclusion.

gdurkee said California had about 1800 cases in 2009 & 2010 with a rate of about 5 cases per 100,000 people. Bad stats. Reported cases are not actual cases. To quote the CDC: not all infected persons are symptomatic, persons who are symptomatic do not always seek medical care, health-care providers do not always include laboratory diagnostics in their evaluation of nonbloody diarrheal diseases, and case reports are not always completed for positive laboratory results or forwarded to public health officials Only about 20,000 of about 1.2 MILLION cases were reported in the US. in 2010. So if, say, 90% of CA case are unreported, the actual number is closer to 16,000 cases, not 1,800.

Out of about 400 PCT thru thru-hikers each year there are usually multiple reports of giardia, commonly in the Sierra. Rockwell said: the risk of contracting giardiasis in the wilderness is similar to that of a shark attack... Untreated Sierra Nevada water should be, almost everywhere, safe to drink—if you “drink smart.” If you don’t “drink smart” you may ingest diarrhea-causing organisms. But it won’t be Giardia. Those are absolutely untrue and deeply irresponsible things to say.
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