Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Norovirus is not just a problem for people on cruise ships. It has also caused outbreaks of gastroenteric illness in the wilderness. In the current issue of Wilderness and Environmental Medicine (2009;20:6-13), Ellen Jones, PhD and colleagues have published an article entitled, "An Analysis of Water Quality in the Colorado River, 2003-04; An Investigation Into Recurring Outbreaks of Norovirus Among Rafters."

As noted in the abstract that appears at the beginning of the article, every year more than 22,000 people raft the Colorado River through the Grand Canyon in Arizona. Since 1994, more than 400 rafters in 6 separate outbreaks have become ill with norovirus while rafting this stretch of river. To try to determine the source of the virus, Colorado River water was collected and sampled during the 2004 rafting season. Water was collected from wastewater treatment plants and from drinking water from the Lee's Ferry launch site. No norovirus was detected during this field sampling.

So, what to make of the fact that people become infected with the virus, but no natural source can be located, at least not in the limited sampling accomplished during 2004? The virus needs to come from somewhere. So, either the investigators did not find a (relatively constant) source, or it is intermittently being introduced into the watershed, or being spread among rafting participants from a member(s) of a trip. Perhaps the river water is contaminated, but then the virus should show up in field tests. Food may be contaminated, but the most likely cause is person-to-person spread, perhaps initiated by contaminated campsites, equipment, or fomites (see below).

The logical conclusion is that all drinking water should be properly filtered and/or otherwise preliminarily disinfected, and then disinfected with heat or a chemical method. Strict handwashing and perhaps even gelling (70% ethanol-based hand-sanitizer) should be undertaken prior to preparing food and eating. For more reasons than norovirus contamination (e.g., the presence of methicillin-resistant Staphylococcus aureus [MRSA]), it's a wise idea to disinfect rafts and rafting equipment, kayaks, and paddling accessories between expeditions.

A fomite is an inanimate object that is capable of transmitting an infectious agent from one person to another. Examples include eating utensils, garments, sleeping bags, paddles, or anything else handled by one person and then handed over to another. The authors point out that since noroviruses are quite resistant to environmental stresses, such as ultraviolet light and heat, and also fairly high concentrations of detergent and chlorine, at a minimum, one should consider cleaning items with detergent followed by disinfection with a detergent/bleach disinfectant (5000 parts per million of bleach) with a contact time of at least one minute.

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Preview the Annual Meeting of the Wilderness Medical Society, which will be held in Snowmass, Colorado July 24-29, 2009.

Join me from January 24 to February 2, 2010 for an exciting dive and wilderness medicine CME adventure aboard the Nautilus Explorer to Socorro Island, Mexico to benefit the Wilderness Medical Society.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.