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Why Rockwell is Wrong about Giardia

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Why Rockwell is Wrong about Giardia

Postby Colter » Sat Feb 16, 2013 6:16 pm

First of all, this isn't a personal attack on Robert Rockwell, because by all accounts he is a great guy. Nor am I insisting everyone treat their water, reasonable people may have different risk assessments.

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.

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

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.

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

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

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 The largest retrospective study of it's kind of which I'm aware is one done in Colorado which showed someone not treating water was 3-5 times as likely to get giardia as one who did treat water and it concluded drinking untreated mountain water is an important cause of endemic infection. http://www.journals.elsevierhealth.com/ ... 105_330%20

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.]

I would enjoy hearing your comments!



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Re: Why Rockwell is Wrong about Giardia

Postby rlown » Sat Feb 16, 2013 6:31 pm

wow! I'm not hiking with you. :D Never had it and hope i never do. We've talked about water treatment to death on this forum. Feel free to use the search option on the top right on filter or water treatment.

Welcome to HST!

Russ
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Re: Why Rockwell is Wrong about Giardia

Postby RoguePhotonic » Sat Feb 16, 2013 6:58 pm

For example, Rockwell says that Sierra water is cleaner than San Francisco city water.


I think this statement would depend on how you look at it. In America we are labeled as having great drinking water out of the tap but I think it's a trade off. Our water is treated so it has no pathogens in it but then most locations in major cities have high levels of heavy metals and other junk that are longer term health issues. Then of course so many areas add toxic waste to the water (sodium fluoride).

I am not the type to say (I have been doing this and i'm fine!). That's not science. But to add to a list for comparison I have only got sick in the Sierra one time with diarrhea that lasted 2 days and I was filtering at the time.

I have spent quite allot of time in the Sierra not filtering and not being careful about where I get my water including my longest run last year of 80 days from the Southern most area of Kings Canyon National Park to Yosemite and all in between and never got sick.

Despite this I will probably still bring a filter this year. At the very least it will save me from having to drink so many water fleas like last year.
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Re: Why Rockwell is Wrong about Giardia

Postby SSSdave » Sat Feb 16, 2013 8:25 pm

I would argue against some of your points while others are uncertain either way. While it is true someone can come down with giardia from a single cyst, very few of us are so sensitive. We humans have an estimated 100 trillion bacteria inside our bodies that collective weigh 2 to 5 pounds of our weight. Those exposed to bad bacteria tend to become resistant to them and my two years in the third world at age 19 probably had an effect. That is why locals down in Mexico don't get Montezuma's Revenge like visiting Anglos.

In any case for this person it does not matter. As a decades old backpacker that only used a water filter religously during a few years during the worst of the hysteria when the NPS/NFS demanded use, I didn't get giardia before filters and haven't since so no reason to change the wise approach to water selection that works.

But thanks for the thread. It reminded me that I at least wanted to buy one of those inexpensive straw filters so just bought one on Amazon. For 2 ounces it will get me through the infrequent situations like last year along Graveyard Meadows where every other step is atop some cow flop.
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Re: Why Rockwell is Wrong about Giardia

Postby Colter » Sun Feb 17, 2013 7:55 am

Thanks for the responses.

On water cleanliness, Rockwell's point was that San Francisco water has more giardia cysts on average than Sierra water. Yet the arriving raw water is still so clean, he says, that the city has a waiver so they don't have to filter. Based on that, most people will likely conclude it makes no sense to filter in the Sierras. What Rockwell doesn't mention is that San Francisco treats their water (currently chlorine, chloramine AND UV light) to make it safe to drink. To me, that qualifies as misinformation.

It might be true that few of us will get sick from a single cyst, but some of us will. Rockwell does his calculations as if it were impossible to contract giardia at the 1-9 cyst level, which is untrue and extremely misleading.

I do think that long term personal experience is meaningful to a degree, but I also think that "past performance does not guarantee future results" for any of us.
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Re: Why Rockwell is Wrong about Giardia

Postby dave54 » Sun Feb 17, 2013 10:13 am

I have not had a serious injury while out hiking and I still carry a first aid kit.

I have never been in a car accident and still religiously wear a seat belt.

I have not had giardia and I still filter.
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Re: Why Rockwell is Wrong about Giardia

Postby maverick » Sun Feb 17, 2013 12:44 pm

Hi Colter,

Welcome to HST!
If you use the "search feature" you will find numerous threads on Giardia and water
treatment, here is just a sample:
viewtopic.php?f=9&t=113&p=597&hilit=+giardia#p597
viewtopic.php?f=1&t=7016&p=49237&hilit=filtering+water#p49237
viewtopic.php?f=1&t=6452&hilit=giardia
HST= Wilderness Adventurer who knows no bounds, except for their own imagination.

Have a safer backcountry experience by using the HST ReConn Form 2.0, named after Larry Conn, a HST member: http://reconn.org
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Re: Why Rockwell is Wrong about Giardia

Postby AlmostThere » Sun Feb 17, 2013 2:41 pm

I'm pretty much a career water-treater because non-backpackers I know who have gotten into Sierra water many times to rescue people have an absurdly high rate of giardia. (They show up, dive in, and drive home - no meals shared, no hand hygiene required.) One I know has had to get medical intervention three times.

I really don't need much convincing, after talking to people who have a history of hospital visits and verified cases. Or my friend's poor pooch who got it drinking from a national forest stream - of course, they graze cows in NF and packers roam freely on the trails everywhere up there, making it pretty certain that I'd much rather filter than drink from open sources.

High elevation sources, I was dubious about. And then I met someone who is now a career water treater after coming home from a high alpine trek where he treated everything below 10,000 feet, and racking up medical treatment costs.

And yes, this is a pretty overdone topic. On which you're not going to convince anyone to shift opinion - some of us have "anecdotal evidence" that's more than enough to get us buying filters. Some of us continue to be asymptomatic and drink from whatever waterway they find. I'd rather not find out that I'm not a carrier who will never develop symptoms the hard way. Too little time, too many things I need to accomplish without wasting a lot of time dealing with giardia. Too easy to just treat the water.
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Re: Why Rockwell is Wrong about Giardia

Postby Colter » Sun Feb 17, 2013 4:44 pm

Actually, these facts have already changed some minds on other forums.

The Rockwell paper is probably the most cited giardia paper (amongst outdoors people) on the internet. To many, it reflects the best science on the topic. However, I think it's easy to show that it's significantly flawed, and that the CDC, EPA, FDA and the California Department of Health are in fact right about the risks of drinking untreated backcountry water, which has been clearly proven statistically, not just anecdotally.

Whether or not to treat/filter is another issue. I realize there is some risk in hiking alone which I do often and I will continue doing so. On the other hand, I will treat my water from here on out to avoid more doctor visits, but that's just my call.
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Re: Why Rockwell is Wrong about Giardia

Postby rlown » Sun Feb 17, 2013 4:53 pm

Personally, I'd rather read some of your trail reports. :)

As AT and Mav point out, the Giardia/Filtration topic is pretty much a done deal here.
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Re: Why Rockwell is Wrong about Giardia

Postby Colter » Sun Feb 17, 2013 5:37 pm

rlown wrote:Personally, I'd rather read some of your trail reports. :)

As AT and Mav point out, the Giardia/Filtration topic is pretty much a done deal here.

I think I've presented some new scientific perspectives. Obviously people are free to read or ignore this thread. I'm not interested in the usual back and forth about personal evaluation of risk, anecdotes and opinions either, but I would like to spark a discussion about the underlying science with those who are interested.

If you prefer, you can read my PCT journal: http://bucktrack.com/PCT.html ;)
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Re: Why Rockwell is Wrong about Giardia

Postby AlmostThere » Sun Feb 17, 2013 5:43 pm

Colter wrote:I think I've presented some new scientific perspectives.


You're free to think that.

I'm not going to alter anything I think or do, just the same, for more convincing (to me) reasons than scientific perspectives.

Frankly, in my profession, I've seen plenty of scientific research debunked and tossed aside. The presence of research says nothing to me unless I have access to the work itself to analyze the actual statistical data and the ways it was gathered - and on this topic, I've got no time or energy or motivation to bother, since I'm treating water regardless. I suspect that I am not alone in this.
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