Giardia: Just the facts m’am

Hi Andrew,

Good job on finding the Derlet paper. Thanks for posting that link. I'd been unable to find it online.

I think your attitude is perfectly rational. Accepting reasonable risks are important in the outdoors and in life in general.

My take-home message from the Rockwell and Welch papers was that the odds of getting giardiasis in the Sierra were virtually zero. That's obviously not the case. I paid attention to my water sources. I got giardiasis.

"So drink freely and confidently" Rockwell says. The science clearly shows that is very bad advice.

Here are some key parts of the Derlet Paper:
Coliform bacteria have been established as indicators of fecal pollution or contamination, including Giardia…Results…Coliforms were found in 9% (4/47) of Wild site samples, 12% (5/42) of Day Hike site samples, and 18% (20/111) of Backpacker site samples.
In contrast, 63% (70/111) of Pack Animal site samples yielded coliforms, and 96% (51/53) of samples from the Cattle areas grew coliforms…
Conclusion.—Surface water from watersheds below cattle areas and those used by pack animals is at high risk for containing coliform organisms. Water from Wild, Day Hike, or Backpack sites poses far less risk for contamination by coliforms…

How much risk is "far less risk?" Hard to say.

"Have you read through the information on the links I posted on this thread 10/12/2012 09:57:15 MDT? It covers much of what we are discussing."

Yes, Buck, I have. Other than citing your own experience and some others at Mammoth Lakes, there is nothing to remotely support yours claims about the high risk of contracting giardia in the Sierra other than one study by Derlet that talks about coliform bacteria in areas where there are stock animals grazing and the Modesto Bee article. Such areas are in no way pristine, and anybody who drinks untreated water in such areas is being, how shall I put this, "less than prudent"?

"Dr. Derlet is considerably more qualified to determine what sources are likely to be pristine than most of us. "What [Derlet] 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.""

"Parts of the Sierra", he says. Of course, but he wasn't referring to giardia, as far as I can tell. Rockwell says the same, a fact you seem to have conveniently overlooked in your debunking. Derlet also published an article in 2006, cited by Paul Johnson in the previous thread you link to, that found 0 coliform in 14 out of 15 samples taken from what I would consider semi pristine areas, such as Rae Lakes, Woods Creek, South Fork Kings River, and even the Kern River. Why would the numbers differ for giardia? Here's the link to the 2006 Derlet article: http://www.highsierrahikers.org/derlet-and-carlson-2006.pdf. I think 2006 is recent enough to have some credibility, don't you?

"The EPA said "Hancock et al. (1997) collected 463 groundwater samples from 199 sites in 23 states in the United States; Giardia cysts were found in 14% of the springs.""

Again, nothing about truly pristine sites in the Sierra.

"The book Nols Soft Paths: Enjoying the Wilderness Without Harming It says "In a study of pristine streams in the Sierra Nevada, Forest Service Hydrologist Thomas Suk and his colleagues found that 35% of the water tested had dormant giardia cysts."

Again, what do they mean by pristine? More areas where cattle and horses are allowed to graze? Specifically which streams?

"You said "In the absence of hard data to support your claim that giardia lurks everywhere, I think you risk doing a similar disservice by spreading fear where there is little, if any, danger." Remember the EPA says "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." They aren't saying all waters all the time, and I'm not either. There's plenty of hard data showing cysts are often found in places people would believe to be pristine, including the Sierra."

The EPA statement, without specific location data, is meaningless to our dialogue. Again, that word pristine pops up. The dictionary says it means unspoiled, which certainly eliminates areas exposed to livestock or large numbers of hikers. Do you make this distinction? Does the EPA?

"My cited studies showed many people get giardiasis on a single trip. Pointing that out isn't paranoia, it's reality."

I would say it one person's view of reality. Mine is considerably different and is very close to Roger Caffin's. I could sum up where I am coming from by saying at this point, a huge +1 to mssrs Caffin, Paul Johnson, and Paul McLaughlin. I couldn't put it any better, and I won't waste my time trying.

"Rockwell said "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." I believed him and got giardiasis after following his advice on my first long hike in the Sierra. He paper is fraught with misinformation of many kinds and his conclusion isn't supported by good science."

I am truly sorry you contracted giardiasis on your first trip to the Sierra. It is a miserable affliction. I know, because I contracted amoebic dysentery on my first trip to India, and I wouldn't wish it on my worst enemy. However, to try to place the blame on Rockwell, which is what you seem to be doing, is bad form, IMO, to say the least. He didn't give people a "get out of jail free" card in his article. He stressed the necessity of evaluating each site and using judgment in deciding whether or not to treat. What he did say was that your chances of contracting giardia in most places IN THE SIERRA is vanishingly small, and nothing you have brought to the discussion makes a strong case otherwise. Even Derlet, in his 2006 article basically backs him up, even if only on coliform bacteria, which is the cause of most backcountry GI illness. You haven't come close to debunking his article, IMO, which is copiously sourced, often with some of the same sources you mention. One more question: Was your illness confirmed with stool sample analysis, preferably ELISA, which Rockwell says is far more accurate than the standard stool sample analysis technique of lookin for cysts? If not, could it not have been a coliform infection? If your doctor just went ahead and treated you for giardia, here is an interesting article:

http://jac.oxfordjournals.org/content/5/2/201.short

Also, you fell ill near Mammoth. Given a 3-25 day gestation period, where were you 25 days prior? or even 14 days. What I am getting at is that you might not even have been in the Sierra when you contracted giardia, if it was giardia.

I'm sorry to be so inquisitive, but I am truly interested in getting to the bottom of this, for my own sake.

Tom,

If we specify that pristine means the absence of pathogens, then, yes, there are is no giardia in pristine areas of the high Sierra. However, pathogens including giardia have been found in areas of the high Sierra and elsewhere that water experts have classified as wild and/or pristine, so I'm not sure what else I can tell you on that issue. If you are saying that the "wilder" an area is the safer the water is likely to be I'd say you are right.

In his paper, Derlet says "Coliform bacteria have been established as indicators of fecal pollution or contamination, including Giardia" so his study is very applicable to Giardia. It is only one part of the evidence because several studies have found giardia cysts in wild/pristine areas in the Sierra. Derlet also said that "One infected head of [Sierra] cattle may excrete 100 million Giardia cysts per day, enough to infect the entire city of Los Angeles" which directly refutes Rockwell's statement: "One conclusion of this paper is that 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."

And can you be more specific in what I "conveniently overlooked?"

Rockwell says "a few Giardia cysts are found in some wilderness waters, with no evidence that it is even remotely a problem." Really? No evidence? How about the several peer reviewed scientific studies to the contrary and the hundreds of reports of waterborne giardiasis from backpackers?

Quotes from conclusions of four peer reviewed scientific papers:
"drinking untreated mountain water is an important cause of endemic infection"
"These surveys show that campers exposed to mountain stream water are at risk of acquiring giardiasis."
"the authors concluded that consumption of local water while participating in outdoor activities, such as camping, was associated with a higher risk of giardiasis than in controls who participated in such activities but did not ingest local waters."
"an outbreak of waterborne giardiasis occurred in a group of 93 university students and faculty participating in a geology field course in Colorado. All cases occurred in one subgroup of persons who were heavily exposed to untreated stream water."

If you think I haven't come close to debunking Rockwell's paper, I adamantly disagree.

I said "My cited studies showed many people get giardiasis on a single trip. Pointing that out isn't paranoia, it's reality."

You said "I would say it one person's view of reality."

So you are claiming my cited scientific studies are "one person's view of reality"? It's hard to know how to respond to that.

You said "You haven't come close to debunking his article, IMO, which is copiously sourced." Sorry, just saying I haven't debunked it is meaningless. You have to give some examples. I've shown that critical points of his paper don't hold up, including a reliance on old data, a misinterpretation of the infectious dose, and much more. Rockwell proudly days that "National Geographic Adventure" magazine verified the findings of his paper. Presumably that's the best he could do. I highly doubt that any public health organizations have verified his findings. The Rockwell paper IS copiously sourced but those papers overwhelmingly refute his conclusions. He has cherry-picked parts of them to put together his paper.

I could sum up where I am coming from… Please do.

Backpacker Magazine, December 2003 has a passage that comes close to summing up my thoughts on the matter. The variable nature of contaminants, and our own bodies, leaves a vast gray area between two extremes. At one end is the paranoid perception that every pristine-looking stream is crawling with microbes, and the other is the blind hope that all water is really as good as it looks. Between these extremes lies the truth.

"However, pathogens including giardia have been found in areas of the high Sierra and elsewhere that water experts have classified as wild and/or pristine, so I'm not sure what else I can tell you on that issue."

The cases you cite all seem to mention areas where livestock are allowed to graze. If you/they consider that to be pristine, I'm not sure there is much to talk about. We are speaking a totally different language. In any case, how someone would drink untreated water in such areas is beyond me. And Mr Rockwell, I'd bet.

"And can you be more specific in what I "conveniently overlooked?"

This, from Rockwell's article. If you hadn't overlooked it, I'll bet you wouldn't have gotten sick.

I started visiting the Sierra Nevada in the early 1950s and have spent much of my free time there. I have never treated the water, and I have never had symptoms of giardiasis as a consequence of my visits. My many similarly active friends and acquaintances also drink the water with no ill effects. But because of other organisms possibly present, we are always careful to “drink smart”:

Drink from large fast-flowing streams whenever possible, preferably those entering from the side rather than those paralleling the trail.
Drinking water from a lake is best advised at the inlet, with the next best place at the hopefully fast-flowing outlet.
Few Giardia cysts survive harsh Sierra winters. Contamination begins essentially anew each year, so springtime water is safer than summer or fall.
Water at higher elevations is safer than lower, partly because of reduced human and animal presence up high, and partly because water flowing to lower elevations picks up more contaminants the more distance it travels.
The colder the water is, the more likely it is freshly melted, meaning less opportunity for contamination.
Because filtration of water through soil removes Giardia cysts, deep well water is considered safe.7 By implication, springs in the wilderness should be, too.
One would think that after a heavy snow year, when streams run full and long, some kind of “flushing out” effect of lakes and streams must be occurring. Conversely, it makes sense to be more cautious in dry years.
Avoid water that likely could have passed through an area subject to heavy human or animal use.
If it doesn’t look good—it’s cloudy or has surface foam—treat it or don’t drink it.

"In his paper, Derlet says "Coliform bacteria have been established as indicators of fecal pollution or contamination, including Giardia" so his study is very applicable to Giardia. It is only one part of the evidence because several studies have found giardia cysts in wild/pristine areas in the Sierra. Derlet also said that "One infected head of [Sierra] cattle may excrete 100 million Giardia cysts per day, enough to infect the entire city of Los Angeles" which directly refutes Rockwell's statement: "One conclusion of this paper is that 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'm happy to hear that, because that means that the semi remote areas in his 2006 study with Carlson were very likely giardia free as well. They represent quite a swath of the Sierra, BTW. Again, you mention studies of wild/pristine areas without specifics and in the same paragraph as infected cattle. Look, Buck, I'm not arguing that areas where cattle graze are free of giardia. What I AM saying is that they are not pristine in any normal sense of the word, and that no one in their right mind
would drink untreated water from them. There is no doubt Mr Rockwell is saying the exact same thing(see my quote above). Where we disagree is that you seem to want to extrapolate from that to the entire Sierra, and I think you are both flat out wrong and are doing Mr rockwell a great disservice in the bargain.

"Rockwell says "a few Giardia cysts are found in some wilderness waters, with no evidence that it is even remotely a problem." Really? No evidence? How about the several peer reviewed scientific studies to the contrary and the hundreds of reports of waterborne giardiasis from backpackers?"

You haven't presented any peer reviewed studies regarding the Sierra that I am aware of, and backpacker reports without supporting lab confirmation are worthless from a scientific standpoint.

"Quotes from conclusions of four peer reviewed scientific papers:
"drinking untreated mountain water is an important cause of endemic infection"
"These surveys show that campers exposed to mountain stream water are at risk of acquiring giardiasis."
"the authors concluded that consumption of local water while participating in outdoor activities, such as camping, was associated with a higher risk of giardiasis than in controls who participated in such activities but did not ingest local waters."
"an outbreak of waterborne giardiasis occurred in a group of 93 university students and faculty participating in a geology field course in Colorado. All cases occurred in one subgroup of persons who were heavily exposed to untreated stream water."

Any references in the peer reviewed studies to the Sierra? Have you taken a look at Mr Rockwell's sources, speaking of studies?

"So you are claiming my cited scientific studies are "one person's view of reality"? It's hard to know how to respond to that."

None of the studies present evidence for the Sierra. When you extrapolate from studies in Colorado, Alaska, B.C., and Utah to the Sierra, it becomes one person's version of reality. In the Sierra, that is.

"You said "You haven't come close to debunking his article, IMO, which is copiously sourced." Sorry, just saying I haven't debunked it is meaningless. You have to give some examples. I've shown that critical points of his paper don't hold up, including a reliance on old data, a misinterpretation of the infectious dose, and much more. Rockwell proudly days that "National Geographic Adventure" magazine verified the findings of his paper. Presumably that's the best he could do. I highly doubt that any public health organizations have verified his findings. The Rockwell paper IS copiously sourced but those papers overwhelmingly refute his conclusions. He has cherry-picked parts of them to put together his paper."

You've shown nothing of the sort, as far as I'm concerned. He said, for instance, that it is theoretically possible to contract giardia from one cyst, but not likely. Do you want to tell me that is misinterpreting the infectious dose? Seriously? As for reliance on old data, do you have any new data FOR THE SIERRA to refute it? Derlets' 2006 study, in fact, supports his position. You are telling me that the sources he references refute his position? Really? Have you read them all?
I find it hard to believe that a scientist with a PhD in Biomechanics would source material that refutes his thesis. I suspect it is you who are doing the cherry picking.

Tom,

You are repeatedly insinuating that Rockwell's paper applies only to the high Sierra in places other than where stock is grazing. This sentence from his paper illustrates that is not true:
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. In some respects, this situation resembles (the threat to beachgoers of) a shark attack… He's talking about the whole country. That is why his paper is quoted by groups from Alaska to the Boundary Waters to the Appalachian Trail.

Tom said: He said, for instance, that it is theoretically possible to contract giardia from one cyst, but not likely. Do you want to tell me that is misinterpreting the infectious dose? Seriously?

Yes, seriously. Elsewhere Rockwell says "10: [cysts] Minimum needed to contract giardiasis." He also uses that number to calculate how much water one would need to drink to get giardiasis in the Sierra, which turns out to be a virtually impossible amount. He also says "There are no documented cases of giardiasis being contracted from such low levels [1 cyst]." Only 5 people have been tested in history at the 1 cyst level, and that was one time. So the test at the one cyst level is statistically inconclusive, at best, and what Rockwell also fails to mention is 100% of people tested at the 10 cyst level got giardiasis, and no one has ever been tested at the 2,3,4,5,6,7,8 and 9 cyst levels. So his calculations for how much water one would have to drink to get giardiasis are bogus. For sure. Not even considering that old studies can't be used to calculate current risk.

You keep saying Derlet's 2006 paper is the latest. It's not. It's his 2008 paper. http://www.ericjlee.com/Articles/Sierra%20Water%205years.pdf That's the most current data we have and the Modesto Bee, not stubbornly arguing their position like you and I are, summed it up thusly (as you recall) bacterial contamination was easily high enough to sicken hikers with Giardia, E. coli and other diseases. Again, specifically talking about the high Sierra. When I was "drinking smart" in the high Sierra and got giardiasis, I drank from a fast moving cold stream and only later noticed that cattle had been in the area. Drinking smart is an educated GUESS. About 10 days later I got sick. If I hadn't read the Rockwell article, I would, for sure, have been treating my water. All of it. And people are perfectly within their rights to not treat water based on their own risk assessments.

Tom You are telling me that the sources he references refute his position? Really?
Really.

He cites the The Bad Bug Book. Center for Food Safety which says
Anyone can get giardiasis, and those at higher risk include hikers, hunters, and others who might drink water from the outdoors
He cites Cyst Acquisition Rate for Giardia Lamblia in Backcountry Travelers
to Desolation Wilderness, Lake Tahoe which showed 5%+ of backpackers got giardia on a single trip. Outside of cattle country if I'm not mistaken.
Rockwell cites Back-country water treatment to prevent giardiasis Obviously not a paper worthy of publication were waterborne giardiasis not a significant problem. As a matter of fact they say [giardiasis} is commonly considered a backpacker's illness.
He cites: An Outbreak of Giardiasis in a Group of Campers which concluded campers exposed to mountain stream water are at risk of acquiring giardiasis.
He cites the Giardiasis Fact Sheet which says
Those at greatest risk are…Backpackers or campers who drink untreated water from lakes or rivers
Rockwell cites the Inyo National Forest water safety advice which says: Many cases of giardiasis have been attributed to untreated water in the Sierra Nevada.
He cites Giardiasis: an elusive cause of gastrointestinal distress which says Prevention for people involved in outdoor sports or recreation and for international travelers includes treatment of all surface water and rigorous personal hygiene.

There are more examples, I'm sure. His most frequently cited source is himself.

"You are repeatedly insinuating that Rockwell's paper applies only to the high Sierra in places other than where stock is grazing. This sentence from his paper illustrates that is not true:
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. In some respects, this situation resembles (the threat to beachgoers of) a shark attack… He's talking about the whole country. That is why his paper is quoted by groups from Alaska to the Boundary Waters to the Appalachian Trail."

I'll give you this one, Buck. He shouldn't have expanded his conclusion beyond the Sierra.

"Yes, seriously. Elsewhere Rockwell says "10: [cysts] Minimum needed to contract giardiasis." He also uses that number to calculate how much water one would need to drink to get giardiasis in the Sierra, which turns out to be a virtually impossible amount. He also says "There are no documented cases of giardiasis being contracted from such low levels [1 cyst]." Only 5 people have been tested in history at the 1 cyst level, and that was one time. So the test at the one cyst level is statistically inconclusive, at best, and what Rockwell also fails to mention is 100% of people tested at the 10 cyst level got giardiasis, and no one has ever been tested at the 2,3,4,5,6,7,8 and 9 cyst levels. So his calculations for how much water one would have to drink to get giardiasis are bogus. For sure. Not even considering that old studies can't be used to calculate current risk."

He is talking about the generally accepted dose, if I'm not mistaken. As for it being virtually impossible to drink the required amount of water to ingest 10 cysts,
he also says that concentrations do vary for a variety of reasoons, as does Roger Caffin, and that it is possible to get 10 or more cysts in a drinkable amount of water, say, for instance, a few feet upstream from where an infected cow dumped a load. I think that is just common sense. That the test at the one cyst level was statistically inconclusive is beside the point. It represents the one time the test was conducted at the level and is the only data we have. that 100% of the people tested at the 10 cyst level got giardia is a pretty good indication of why that is the generally accepted amount required for infection, until tests at 9, 8, 7…..prove otherwise. The same goes for his calculations for the amount of water required. All of this is an exercise in probability anyway, as everybody should realize that concentrations vary all over the place for any number of reasons, one of which I gave, above.

"You keep saying Derlet's 2006 paper is the latest. It's not. It's his 2008 paper. http://www.ericjlee.com/Articles/Sierra%20Water%205years.pdf That's the most current data we have and the Modesto Bee, not stubbornly arguing their position like you and I are, summed it up thusly (as you recall) bacterial contamination was easily high enough to sicken hikers with Giardia, E. coli and other diseases. Again, specifically talking about the high Sierra. When I was "drinking smart" in the high Sierra and got giardiasis, I drank from a fast moving cold stream and only later noticed that cattle had been in the area. Drinking smart is an educated GUESS. About 10 days later I got sick. If I hadn't read the Rockwell article, I would, for sure, have been treating my water. All of it. And people are perfectly within their rights to not treat water based on their own risk assessments."

Does his 2008 paper invalidate his 2006 paper? No, it does not. Almost none of the non cattle/horse sites have coliform bacteria. Do some? Yes. So it boils down to risk assessment, i.e. DRINK SMART!

If you drank before assessing the water source you were using, you weren't drinking smart. Period. Signs of cattle are pretty obvious, IME. Sorry to be so frank, but that is what your post is telling me. Your sickness came on 10 days later, which would have put your where? Just curious. Way south in Kern country, south of Sequoia NP boundary?

You are absolutely correct, IMO, about being within your rights not to treat your water. But you are also responsible for the consequences, not Mr Rockwell.

BTW, just so you know: I got sick on a trip this summer, down in LeConte Canyon, precisely because I didn't do a proper water source assessment. Like yourself, I noticed the manure after drinking. Fortunately, it came on almost immediately, and I was able to treat it with a combination of Immodium and Bactrim, which indicates that it was coliform in nature. I got off lucky. The difference between you and me is that I didn't blame Rockwell for my own screw up. IMO, there's a lesson here for you, Buck, and I mean that with absolutely no malice. You're a bright young guy, but I think you'd be a lot better off applying your considerable intellect to rationally analyzing what happened and adjusting your protocols accordingly, instead of trying to foist the blame off on the author of one of the best articles I have seen on the subject of water hazards in the Sierra. My 2 cents.

Tom

Thanks for conceding the Sierra vs US point. On forums it's traditional to never concede a point!

I definitely made a mistake, but it was not believing my own experience in previously getting lab confirmed giardiasis, along with discounting the recommendations of the CDC and EPA which I'd already read. If I had more carefully researched the Rockwell paper I wouldn't have believed it. Caveat emptor.

The only way to make a rational risk assessment is to have some idea of the odds of a negative consequence occurring. For example, I don't worry about wolf attack because the odds in the U.S. are virtually zero. I have to know if that's true before I can decide if I should carry "wolf spray."

Rockwell said "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." ALMOST CERTAINLY. I must be mighty unlucky.

Here's a typical take-away message from the Rockwell paper posted on another forum: "Rockwell believes that water filters have no value in the Sierra Nevada, and by implication, also, in many other areas." I have heard from other people who specifically said they didn't treat based on the Rockwell paper, then got giardiasis.

If I hadn't read the Rockwell paper I would have treated all my water like I had for the prior 20 years. I had walked along the stream without seeing any sign of cattle. I guarantee that the typical "drink smart" devotee would also have been chugging the water of that fast, clear stream. The trouble with "drinking smart" is that all too commonly there's an issue with the water we don't see until moving on a few hundred yards. There are even more issues that are impossible to see at all.

The reason I'm pressing this issue is that other people will be getting sick too if they read and believe Rockwell's paper. That is more important than my ego or Rockwell's.

The "drink smart" philosophy is clearly risky. Both of us have gotten sick from water recently following that practice. "Almost certainly" we won't get giardiasis is baloney.

"So drink freely and confidently" Rockwell says. Freely: adverb. "Without restriction" Conflicts a bit with drink carefully in my opinion.

"Thanks for conceding the Sierra vs US point. On forums it's traditional to never concede a point!"

Never a problem for me, Buck. I'm a lot more interested in getting at the truth than preserving what's left of my rapidly shrinking ego at this point in my life. Your point was well taken.

"Caveat emptor."

Always a wise policy, IMO. Lord knows I've learned that the hard way, on more occasions than I'd like to admit.

"The only way to make a rational risk assessment is to have some idea of the odds of a negative consequence occurring." I'd say it's one of the ways. My approach is quite different. I start by considering the consequences if an undesirable event were to occur. If they are so dire that I could not bear them, I don't much care what the odds are, I simply will not expose myself to the possibility, and to he!! with the odds. But that is just me. Gettin' old, I guess.

"Rockwell said "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." ALMOST CERTAINLY. I must be mighty unlucky"

For me the operative word here is "almost". His article has so many caveats to the idea of certainty that I just ignored it. The message I came away with is to pay attention to where you drink and the odds will be so much in your favor as to make it "almost" certain that you will not contract giardiasis. But odds are just that: odds. If you are the one who contracts giardiasis, the odds have just become 100 in 100, which is why I don't pay much attention to odds.

"Here's a typical take-away message from the Rockwell paper posted on another forum: "Rockwell believes that water filters have no value in the Sierra Nevada, and by implication, also, in many other areas." I have heard from other people who specifically said they didn't treat based on the Rockwell paper, then got giardiasis."

True, but he also recognizes that some people may decide to treat, and expresses no opposition to that. He recognizes it as an inherently individual decision, as is the decision not to treat. He even goes thru some of the treatment options available, IIRC.

"The reason I'm pressing this issue is that other people will be getting sick too if they read and believe Rockwell's paper. That is more important than my ego or Rockwell's."

Given that a number of people have interpreted the article as you did, I'd say you're performing a public service. Perhaps, if Mr rockwell is following this thread, he might even consider clarifying certain portions of the article to make it more suitable for a wider audience than he originally intended. Have you thought of trying to contact him. He sounds like a pretty reasonable typpe to me, and I'll bet he would at least hear you out.

"The "drink smart" philosophy is clearly risky. Both of us have gotten sick from water recently following that practice."

I'm going to have to exclude myself from this statement. I don't think I drank smart at all, and I paid the price. I'm usually a lot more cautious than I was that day. It is the first time in nearly 40 years that I have ever gotten diarrhoea in the Sierra, and I have nobody but myself to blame.

"Conflicts a bit with drink carefully in my opinion."

He could probably have expressed it a bit more clearly. I think he assumed his earlier admonishment to drink smart would carry thru to the end; still, it might have been better to reemphasize it at the end, as well.

Worthwhile dialogue, IMO. Thanks for engaging, Buck.

Tom