Why Rockwell is Wrong about Giardia
Posted: 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" onclick="window.open(this.href);return false; 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" onclick="window.open(this.href);return false;
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" onclick="window.open(this.href);return false; 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" onclick="window.open(this.href);return false;
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!
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" onclick="window.open(this.href);return false; 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" onclick="window.open(this.href);return false;
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" onclick="window.open(this.href);return false; 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" onclick="window.open(this.href);return false;
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!