The popularity of backcountry travel has brought to public attention concerns over the safety of wilderness water consumption. Epidemiologic studies are limited, but place the incidence of wilderness-acquired diarrhea (WAD) in the range of 3–5%. Although the United States Forest Service and National Park Service focus efforts on disinfecting water to prevent giardiasis, the pathogen may only account for a small proportion of diarrheal cases in backcountry travelers. Stool specimen analysis from symptomatic recreationalists suggests bacteria and viruses to be more frequent isolates. A reasonable estimate of etiology can be made based upon the expedition length. On short trips (less than 7–10 days), symptomatic diarrhea will be due to viral or bacterial pathogens and can be treated empirically with agents proven of benefit for management of traveler's diarrhea. For longer trips, illness attributable to Giardia lamblia complicates empiric therapy. Backcountry travelers should filter water to remove protozoan cysts. This should be followed by halogenation to disinfect against bacterial and viral pathogens.
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