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Wilderness diarrhea (WD), also called wilderness-acquired diarrhea (WAD) or backcountry diarrhea, is a variety of traveler’s diarrhea (TD) in which backpackers, hikers, campers and other outdoor recreationalists are infected during temporary visits to relatively remote natural areas. Risk factors include drinking untreated surface water and failure by the individual and his or her companions to maintain personal hygiene practices and clean cookware. Most cases are self-limited and the cause is most often never known.
Some medical and public health researchers believe that the risks of WD have been over-stated and are poorly understood by the public (see Controversy section below).
Names and definitions
As a variety of travelers' diarrhea, "wilderness diarrhea" is a form of infectious diarrhea, itself classified as a type of secretory diarrhea. These are all considered forms of gastroenteritis.
The concept of "wilderness diarrhea" has emerged in the context of North American recreationalists visiting nature reserves or wilderness areas, and may be extended to similar areas in other non-tropical developed countries (western Europe, parts of Australia, etc.). It is less applicable, however, to remote areas of developing countries, because of very different pathogens likely to be encountered there, relative to North American wilderness areas.
The term "backpacker’s diarrhea" might be an appropriate synonym for "Wilderness Diarrhea," but medical literature has traditionally reserved that term, with fair consistency, for giardiasis — a specific cause of "wilderness diarrhea."
Degree of risk
A survey of long-distance hikers on the Appalachian Trail (AT) by D.R Boulware of the University of Minnesota, found that 45 percent of participants who consistently treated water later suffered from diarrhea, compared with 69% of those who inconsistently treated water. Boulware associated "good hygiene" with a decreased risk and a second Boulware survey, also on the AT, found similar results. Both surveys relied solely on self-diagnosis and self-reporting by participants, and implied that all cases of reported illnesses were caused by infection.
An lower infection rate among backpackers of about 3% to 4% was inferred by two other studies that each included follow-up work with participants, according to a review by Steven Zell of the University of Nevada Medial School . Zell reviewed a third study involving one large group of student hikers that suggested an infection rate of 14% within that group.
Giardia lamblia, a common cause of WD, does not tolerate freezing and can remain viable for nearly three months in river water when the temperature is 10°C and for about one month at 15–20°C in lake water. Cryptosporidium, another important WD pathogen, has been shown to survive in cold waters (4°C) for up to 18 months, and can even withstand freezing, although its viability is thereby greatly reduced..
Many other varieties of diarrhea-causing organisms, including Shigella and Salmonella typhi, and hepatitis A virus, can survive freezing for weeks to months. Virologists believe that all surface water in the United States and Canada has the potential to contain human enteroviruses, a cause of diarrheal disease.
Causes
By far the most common causes of WD are Giardia and Cryptosporidium according to Howard Backer in the textbook Wilderness Medicine, although several other organisms may play a larger role than generally believed. Other infectious agents include Campylobacter, hepatitis A virus, hepatitis E virus, enterotoxogenic E. coli, e. coli 0157:H7, Shigella, and various enteric viruses. More rarely, Yersinia enterocolitica, Aeromonas hydrophila, and Cyanobacterium may also cause disease.
There are three vectors for human infection by Giardia and other infectious diarrhea: contaminated food, water, and fecal-oral transmission. It may be difficult to causally associate a particular case of diarrhea with a recent visit to the wilderness, because incubation of the disease caused by infection can vary widely, up to several weeks or more, while sources of infection outside the wilderness can include public water supplies, swimming pools, contaminated food and hand-to-mouth fecal transmission in many different potential circumstances that are commonly encountered.
Giardia is ubiquitous outside of wilderness settings, and may affect 7.5 million Americans at any one time, according to a report in the New York Times According to a different estimate, about 7% of Americans may carry the disease, although as few as 5% of an infected population may develop symptoms. More than 34,000 cases were reported to state health departments in 1991, of which 19 outbreaks were waterborne, and two affected backpackers or campers. .
Symptoms
The incubation period for giardiasis averages about 14 days and that of cryptosporidiosis about seven days. Certain other bacterial and viral agents have shorter incubation periods, although hepatitis may take weeks to manifest itself. The onset usually occurs within the first week of return from the field, but may also occur at any time while hiking.
Most cases begin abruptly and usually result in increased frequency, volume, and weight of stool. Typically, a hiker experiences at least four to five loose or watery bowel movements each day. Other commonly associated symptoms are nausea, vomiting, abdominal cramping, bloating, low fever, urgency, and malaise, and usually the appetite is affected. The condition is much more serious if there is blood or mucus in stools, abdominal pain, or high fever. Dehydration is a possibility. Life-threatening illness in the contect of WD is extremely rare.
Treatment
WD is typically self-limited, generally resolving without specific treatment. Oral rehydration therapy with rehydration salts is often beneficial to replace lost fluids and electrolytes. Clear, disinfected water or other liquids are routinely recommended.
Hikers who develop three or more loose stools in a 24-hour period — especially if associated with nausea, vomiting, abdominal cramps, fever, or blood in stools — should be treated by a doctor and may benefit from antibiotics, usually given for 3–5 days. Alternately, a single dose azithromycin or levofloxacin may be prescribed. If diarrhea persists despite therapy, travelers should be evaluated and treated for possible parasitic infection.
There is no effective antibiotic against Cryptosporidium, which can be quite dangerous to patients with compromised immune systems.
Prevention
Authoritative guidelines caution that safety judgments cannot reliably be made based on the mere appearances of a water source. One key to prevention is therefore various filters and chemical treatments. (see Portable water purification). The choice depends upon the number of people involved, space and weight considerations, the quality of available water, personal taste and preferences, and fuel availability. Careful attention to personal hygiene can also help prevent the spread of infection..
For long-distance backpacking, water filters may be preferred over chemical disinfectants, because they are more likely to be persistently and correctly used. Inconsistent use of iodine or chlorine may be due to disagreeable taste, impatience with extended treatment time or excessive complexity due to water temperature and turbidity.
Because methods based on halogens do not kill Cryptosporidium, and because filtration misses some viruses, the best protection may require a two-step process of either filtration or coagulation-flocculation, followed by halogenation. Boiling is effective in all situations, but won't improve the water's taste.
Iodine resins, if combined with microfiltration to remove resistant cysts, are also a viable single-step process, but may not be effective under all conditions. New one-step techniques using chlorine dioxide, ozone, and UV radiation may prove effective, but still require validation.
Controversy
Researcher: 3% Infection Rate Creates 'Hydrophobia'
Steven C. Zell of the University of Nevada School of Medicine offers an estimate based on his review of several studies, that diarrhea is acquired by wilderness travelers in North America at a rate of between 3 and 4.5 percent , although he notes that information on the subject is limited "because most studies rely upon observation and fail to adhere to the principles of basic epidemiological research."
Zell says water disinfection is recommended, but calls this decision "an individual matter" and suggests that more research is needed. "If Giardia lamblia is an uncommon isolate and WAD (wilderness-acquired diarrhea) is infrequent, then it may not be cost effective to recommend filtering for recreationalists involved in short-duration trips," Zell says, adding that current warnings by the U.S. Park and Forest services have created "hydrophobia" among backcountry travelers, and "misplaced concern" about the safety of wilderness water has "led to anecdotes about dehydration in recreationalists at high altitude requiring emergent evacuation."
Tulane Scientist Screens 104 Articles
Timothy P. Welch of Tulane Medical School, performed a meta-analysis, with an initial screening of 104 articles, in which nine met inclusion criteria for epidemiological analysis. Separately (with Thomas R. Welch) he surveyed state health departments in the United States. Based on these projects, T.R. Welch, of the Children's Hospital of Cincinnati, concluded that "no studies suggest that North American wilderness waters are a source of bacterial enteritis," and that water disinfection is generally unnecessary.
Of the nine articles that T.P Welch analyzed in-depth, neither of two case reports (report of the diagnosis, treatment, and follow-up of an individual patient) met the criteria of the Centers for Disease Control for waterborne disease outbreak. Two "prospective" studies (data on subjects who were followed forward in time) showed no significant association of backcountry water with infection. Of four studies that included control groups, none showed a significant relationship between backcountry water and infection.
34,348 Cases; 2 Among Campers
In a separate project, 48 of the 50 state health departments in the United States responded to a questionnaire about giardiasis. The survey found 34,348 cases reported during 1991. Nineteen were attributed to contaminated drinking water; two were reported among campers and backpackers.
T.R. Welch says education aimed at stopping hand-to-mouth spread is the key to preventing infection. "Diluting this message with unfounded concerns about wilderness water quality or the relative merits of various water-treatment methods serves no useful purpose," Welch writes.
U.C. Scientist Tests 1,000 Samples
Robert W. Derlet of the University of California-Davis School of Medicine and affiliate faculty member of the school's John Muir Institute of the Environment, estimates that he has tested about 1,000 water samples from the Sierra Nevada to date in what he expects will become a 20-year study. "I, along with other scientists believe that the risk of Giardia has been well overstated," says Deret, adding that "If one wants to be entirely safe, one could purify water, but my suspicion is that perhaps less than 1% of streams in the Sierra would have Giardia significant enough to cause infection in humans."
Derlet says water in remote, less-traveled regions of the Sierra is usually free of waterborne pathogens (giardia lamblia, cryptosporidium parvum, et al.). He and various associates routinely drink untreated water in remote regions. Derlet adds that areas affected by cattle and livestock do present risk, and water there should be disinfected. In high-elevation regions of the Sierra, however, "I'd say there is less than a one in 100 chance that a person would get sick drinking untreated water" from side streams, Derlet says.
Wilderness Giardia with particular attention to the Sierra Nevada
About 7 percent of Americans are infected with giardiasis (mostly asymptomatic) and Giardia and other intestinal bugs are mainly spread by fecal-oral or food-borne transmission.
A survey of 64 sites completed in 1984 found between 0.108 and 0.003 giardia cysts per liter. Another survey completed in 1990 of three sites on 10 different dates, found concentrations between 0.0 and 0.062 cysts per liter. In comparison, the San Francisco public water supply has, on occassion, contained 0.12 cysts per liter, and that the Los Angeles Aqueduct averages 0.03 cysts per liter. The city of Fairfield, 45 miles northeast of San Francisco, reported that Giardia cysts were detected three times in 2001 at levels of 0.19, 0.21 and 0.50 cysts per liter, and at these levels, the source water is considered an insignificant risk for giardiasis. Drinking 89 liters of water with 10 cysts per liter would result in a 50 percent chance of contracting giardiasis, with a high probability that any resulting disease would be asymptomatic.
Medical Texts Stand Pat On Disinfection
Despite this research, two standard textbooks on backcountry medical issues continue to promote water disinfection as a key means of preventing infection. Wilderness Medicine, edited by Paul S. Auerbach, describes various commercial water treatment devices in detail, and says that most infectious diarrhea acquired in the U.S. wilderness is from water-borne pathogens, and that effective prevention therefore requires treatment of drinking water as well as proper sanitiation. .
In a 2008 online interview, Auerbach likened drinking untreated water to Russian roulette, adding that while research has shown Giardia in wilderness water sources is "probably not as prevalent as once believed, as researchers like Derlet have shown, but it's still present". The author of the book's relevant chapter, Howard Backer, told the same publication that if a wilderness visitor is confident of untainted alpine water, "you're probably safe to drink it untreated," but that in areas with significant human or animal activity, treatment is critical in prevention..
The text Medicine for Mountaineering and Other Wilderness Activities , maintains that contamination of U.S. backcountry water sources is widespread and that disinfection is necessary, although elsewhere the same work notes that "exaggerated concern" has been raised about the issue: "Government agencies...have filtered hundreds of gallons of water from wilderness streams, found one or two organisms (far less than enough to be infective), and erected garish signs proclaiming the water hazardous".
See also
References
- Zell, Steven C. (1992), “Epidemiology of Wilderness-acquired Diarrhea: Implications for Prevention and Treatment”, Journal of Wilderness Medicine 3, 241-249.
- “Diarrhea is a common illness of wilderness travelers, occurring in about one third of expedition participants and participants on wilderness recreation courses. The incidence of diarrhea may be as high as 74% on adventure trips. …Wilderness diarrhea is not caused solely by waterborne pathogens, … poor hygiene, with fecal-oral transmission, is also a contributing factor.” Hargreaves, Joanna S. (2006), “Laboratory Evaluation of the 3-Bowl System Used for Washing-Up Eating Utensils in the Field”, Wilderness and Environmental Medicine, Vol. 17, No. 2, pp. 94–102.
- Boulware DR, Forgey WW, Martin WJ 2nd (2003). "Medical Risks of Wilderness Hiking". Am J Med. 114 (4): 288–93. PMID 12681456.
{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - ^ Boulware DR (2004). "Influence of Hygiene on Gastrointestinal Illness Among Wilderness Backpackers". J Travel Med. 11 (1): 27–33. PMID 14769284.
- Dickens DL, DuPont HL, Johnson PC (1985), "Survival of Bacterial Enteropathogens in the Ice of Popular Drinks", JAMA; 253:3141–3.
- Backer, Howard (2000), "In Search of the Perfect Water Treatment Method", Wilderness and Environmental Medicine, 11:1-4.
- Gerba, C and J Rose (1990), "Viruses in Source and Drinking Water", In: McFeters G, ed., Drinking Water Microbiology, New York, New York: Springer-Verlang, pp 380-399
- White, G (1992), Handbook of Chlorination, 3rd edition, New York, New York: Van Nostrand Reinhold.
- Backer, Howard D. (2007), “Field Water Disinfection”, In: Auerbach, Paul S. (editor), Wilderness Medicine, 5th edition, Philadelphia, Pennsylvania: Mosby Elsevier, pg 1369.
- Sanders JW, Frenck RW, Putnam SD; et al. (2007). "Azithromycin and Loperamide are Comparable to Levofloxacin and Loperamide for the Treatment of Traveler's Diarrhea in United States Military Personnel in Turkey". Clin Infect Dis. 45: 294–301. doi:10.1086/519264.
{{cite journal}}: Explicit use of et al. in:|author=(help)CS1 maint: multiple names: authors list (link) - Backer, Howard (2002), "Water Disinfection for International and Wilderness Travelers", Clinical Infectious Diseases; 34:355–64.
- Welch TP (2000), "Risk of Giardiasis from Consumption of Wilderness Water in North America: A Systematic Review of Epidemiologic Data", Int J Infect Dis; 4(2):100-3.
- Welch, Thomas R. (2004), “Evidence-Based Medicine in the Wilderness: The Safety of Backcountry Water”, Wilderness and Environmental Medicine; 15, 235 237
- ^ Giardia Lamblia and Giardiasis by Robert L. Rockwell, June 4, 2003, Loma Prieta Chapter of the Sierra Club website. Accessed Nov 6, 2006.
- Adachi, Javier A., Howard D. Backer, and Herbert L. Dupont (2007), “Infectious Diarrhea from Wilderness and Foreign Travel”, In: Auerbach, Paul S. (editor), Wilderness Medicine, 5th edition, Philadelphia, Pennsylvania: Mosby Elsevier, pg 1418.
- Seattle, Washington: The Mountaineers Books, 5th edition, 2001