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" onclick="window.open(this.href);return false; ... &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" onclick="window.open(this.href);return false;
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" onclick="window.open(this.href);return false; ... 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."
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
