Wilderness Acquired Diarrhea - Epidemiology

Epidemiology

The risk of acquiring infectious diarrhea in the wilderness arises from inadvertent ingestion of pathogens. Various studies have sought to estimate diarrhea attack rates among wilderness travelers, and results have ranged widely. The variation of diarrhea rate between studies may depend on the time of year, the location of the study, the length of time the hikers were in the wilderness, the prevention methods used, and the study methodology.

The National Outdoor Leadership School (NOLS), which emphasizes strict hand-washing techniques, water disinfection and washing of common cooking utensils in their programs, reports that gastrointestinal illnesses occurred at a rate of only 0.26 per 1000 program days. By contrast, studies of hiking trips on the Appalachian Trail that averaged almost 5 months, reported that more than half of the hikers experienced at least one episode of diarrhea that lasted an average of 2 days. The occurrence of diarrhea was positively associated with the duration of exposure in the wilderness. A number of behaviors each individually reduced the incidence of diarrhea: treating water; routinely washing hands with soap and water after urination (as did after defecation); cleaning cooking utensils with soap and warm water; and taking multi-vitamins.

A variety of pathogens can cause diarrhea, and most cases among backpackers appear to be caused by bacteria from feces. A study at Grand Teton National Park found 69% of diarrhea affected visitors had no identifiable cause, that 23% had diarrhea due to Campylobacter and 8% of patients with diarrhea had giardiasis. Campylobacter enteritis occurred most frequently in young adults who had hiked in wilderness areas and drunk untreated surface water in the week prior. In another study, there were no identifiable cases of giardiasis.

Fecal-oral transmission may be the most common vector for wilderness acquired diarrhea. There are differing opinions regarding the importance of routine disinfection of water during relatively brief backcountry visits.