Wilderness-acquired diarrhea

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.

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 term may be applied in various remote areas of non-tropical developed countries (U.S., Canada, western Europe, etc.), but is less applicable in developing countries, and in the tropics, because of very different pathogens likely to be encountered there.

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."

Causes

Infectious diarrhea acquired in the wilderness is caused by various bacteria, viruses and parasites, the most common of which are thought to be Giardia and Cryptosporidium. Other infectious agents may play a larger role than generally believed [[[1]] and include Campylobacter, hepatitis A virus, hepatitis E virus, enterotoxogenic E. coli, e. coli 0157:H7, Shigella, and various viruses. More rarely, Yersinia enterocolitica, Aeromonas hydrophila, and Cyanobacterium may also cause disease. Vectors for all of these causes are limited to fecal-oral transmission, water, and contaminated food. The major factor governing pathogen content of surface water is human and animal activity in the watershed..

Giardia requires an incubation period of normally one to two weeks (average seven days) to develop into giardiasis, [2] and Criptosporidium two to 10 days (average seven days) to become cryptosporidiosis. [3] Certain other bacterial and viral agents have shorter incubation periods, although hepatitis may take weeks to manifest itself.

In a study of causes of diarrhea at Grand Teton National Park, visitors suffering from active gastrointestinal complaints were invited to a free clinic. Of 178 people tested, 69% had no identifiable pathogens. Campylobacter was the most common agent isolated at 23%, followed by Giardia at 8%. Salmonella and Shigella were not isolated. Campylobacter enteritis occurred most frequently in young adults who had been hiking in wilderness areas and was significantly associated with drinking untreated surface water in the week before illness [4]

Other significant causes of diarrhea are non-infectious, and include medications, stress, or a change in eating or exercise patterns. [5].

It may be difficult to causally associate a particular case of diarrhea with a recent wilderness trip lasting only a few days because the incubation time may take longer than the length of time of the trip. Studies of long trips into the wilderness, where the trip time is much longer than the mean incubation time of the disease, are less susceptible to these types of errors since the diarrhea is more likely to occur while the person is still in the wilderness . In assessing a suspected case of wilderness diarrhea, it is helpful to view the disease within the larger context of intestinal complaints. Within any given four-week period, as many as 7.2% of Americans may experience some form of infectious or non-infectious diarrhea [6].

There are an estimated 99 million annual cases of intestinal infectious disease in the United States [7], The most common causes in the U.S. population are viruses, followed by bacteria and parasites, including Giardia and Cryptosporidium. Giardia alone may infect up to 10% of Americans at any one time, but because most carriers are asymptomatic, [8], there are only an estimated 2 million cases of symptomatic giardiasis annually in the United States [9], spread mostly by fecal-oral or food-borne transmission.

Giardia lamblia does not tolerate freezing and can remain viable for nearly three months in river water when the temperature is 10°C and about one month at 15–20°C in lake water. Cryptosporidium, another 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 all surface water in the United States and Canada has the potential to contain human viruses, which cause a wide range of illnesses including diarrhea, polio and meningitis.

Degree of risk

The risk of acquiring infectious diarrhea in the wilderness arises from inadvertent ingestion of pathogens. Studies have been done to estimate diarrhea rates of wilderness travelers but a number of these have either focused on only one pathogen, giardia lamblia, or provided scant data.

Rate of Infection Studies

Gastrointestinal illnesses occurred at the rate of 0.26 per 1,000 days in the field among National Outdoor Leadership Schools participants in 2002-2005, and 0.20 incidents per 1,000 days during the 1999-2002 period. These rates had declined from 0.44 per 1,000 days in the 1984-189 time period. Program duration varied from two weeks to three months in various wilderness settings primarily in North America, but also in South America, Asia, and Australia. NOLS instructors emphasize water treatment and hygiene. The complaints amounted to 23% of all illness reported in the programs during 2002-2005[10].

A study of 280 long-distance hikers on the Appalachian Trail hikers. who each logged an average 139 hiking days found that diarrhea was experienced by 56% of the participants. Those who consistently treated their water had a diarrhea rate of 45% compared to 69% for those who did so inconsistently. A rate of 86% was found among those who drank untreated surface water (streams or ponds) more than several times a week. Those who washed their hands with soap and water routinely after defecation had a rate of 36%, compared with 59% for those who didn't.

A separate 1992 questionaire survey of 180 hikers who completed the Applalachian trail [11] found that 63% of subjects reported having diarrhea at least one time during the course of their trip. In 58% of these cases, the duration of the diarrhea was two days or less. Only 7% of all subjects drank exclusively from protected water, with the majority consuming unprotected or untreated water about once a month. There were no significant differences in the frequency of diarrhea between those who drank untreated water and those who treated their water. Authors speculated that the lack of correlation was because of the small size of the study, or incorrect use of filters or disinfectants. Authors also cited an earlier study suggesting that inadequately prepared or unrefrigerated food is a common cause of gastroenteritis in campers.

A questionaire of 155 backpackers who completed the Long Trail in Vermont was analyzed in 1993 and found 10.7% of 74 through-hikers and 3.8% of 76 section hikers reported gastrointestinal complaints. [12] Through hikers reported an average of 25 days to complete the trail; section hikers completed the trail in an average of 4.7 years. The 270-mile Long Trail intermittantly traverses wilderness settings. Authors speculated that through-hikers had more opportunity than section hikers to ingest contaminated food and water.

Four separate field studies were reviewed in 2000 by Steven Zell of the University of Nevada's medical school [13] The studies's separate findings on infection rates ranged from 65% to 3%. The studies, two of which included stool sampling, were in the Uintah and Escalante regions of Utah and in Rocky Mountain National Park in Colorado and involved from 53 to 160 subjects. The hike-duration in one of the studies was two weeks. Duration wasn't specified in the other three studies. Zell concluded that the general rate of infective wilderness diarrhea "is probably less than 10%, with scant data placing it in the 3% to 5% range."

Howard Backer, author of the water disinfection chapter of a standard reference work Wilderness Medicine, said in an editorial on Zell's project that he agreed "with much of [Zell's] risk analysis." Backer added that in his view, studies have variously found attack rates among backcountry users range from 5% to 70%, but that only 40% of infections are symptomatic. [14]. In the editorial, Backer said "there is much misunderstanding, verging on paranoia, about the risk of acquiring diarrhea from microorganisms resident in wilderness water," and that fecal-oral transmission may be the most common vector for backcountry Giardia infection. Backer, however, disagreed with Zell's suggestion that routine disinfection of water may be unwarranted during relatively brief backcountry visits.

An additional study of 41 backpackers in California's Sierra Nevada conducted later by Zell and the U.S. Geological Survey, Water Resources Division, found a Giardia infection rate of 5.7% in stool samples, but no symptomatic giardiasis. [15] A further 16.7% of subjects in this study developed mild gastrointestinal illness, but no Giardia infection. Duration of hikes wasn't specified. Water sampling from three popular stream sites within the study area revealed cyst contaminations in the single digit range for every 100 gallons filtered. Ingestion of 10 cysts is considered a minimum infective dose.

A survey of available literature was conducted in 2000 by TP Welch of the Tulane School of Public Health. Of 104 articles identified in the initial screening, nine met the inclusion criteria. In the articles analyzed, 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.

In a 1991 giardiasis survey of 48 state health departments in the United States, 34,348 cases were reported. Of these, 19 were attributed to contaminated drinking water and 2 were reported among campers and backpackers.

Backcountry Water Quality Surveys

Other sampling surveys have focused on micro-organism content of backcountry water.

Between 0.108 and 0.003 Giardia cysts per liter of water were measured in a 1984 survey of 18 backcountry sites in California's Sierra Nevada. The same survey detected no Giardia at 66 additional sites. Ingesting 10 Giardia cysts is regarded in the minimum infective dose. Another survey completed in 1990 of three Sierra Nevada sites on 10 different dates, found concentrations between 0.0 and 0.62 cysts per liter.[[16]].

An additional survey by Backpacker Magazine of several backcountry sites was completed in 2003. The highest concentration that survey found was 1.5 Giardia cysts per liter. [17].

A further survey of 23 sites in the Sierra Nevada in 2003 sought to mesure coliform bacteria, used as indicators of fecal pollution. Coliforms were detected at eight of the sites. [18]. Very low levels were measured in six of eight sites. Two sites had moderate levels. Author Robert Derlet of the University of California Davis medical school expressed the view that "bacteria, and not protozoa such as Giardia, pose a greater risk of causing water-borne disease in humans."

Derlet performed a similar survey in 2007 of 37 sites in Kings Canyon and Sequoia national parks and found coliforms at 14 sites. None of the 11 sites classified as wild areas had coliforms; two of 12 sites classified as backpack and day-hike areas had coliforms and 12 of 14 sites classified as pack animal areas had coliforms. [19] Data by risk category was consistent with prior studies in the immediate region, as well as data from the entire Sierra consisting of nearly 600 samples analyzed by Derlet from 2001-2007. Elsewhere, the author expresses the view that the risk of giardiasis from backcountry water has been "well over-stated." [20] and that "perhaps less than 1% of streams in the Sierra would have Giardia significant enough to cause infection in humans."

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 coming from 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

Since WD can be caused by fecal-oral transmission, contaminated water, and contaminated food, prevention methods should address these causes. Also it was found that on very long trips, taking multivitamins was associated with a reduction of WD.

The risk of fecal-oral transmission of pathogens can be reduced by good hygiene. This includes: washing hands after urination and defecation; and washing eating utensils with warm soapy water. Additionally a three-bowl system can be used for washing eating utensils.

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. 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. Careful attention to personal hygiene can help prevent the spread of infection.

In a study of long-distance backpacking, it was found that water filters were used more consistently than chemical disinfectants. Inconsistent use of iodine or chlorine may be due to disagreeable taste, extended treatment time or treatment complexity due to water temperature and turbidity.

Because methods based on halogens, such as iodine and chlorine, 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.

Ultraviolet (UV) light for water disinfection is well established and widely used for large applications, like municipal water systems. A small portable UV device, called a Steri-pen, is now available for hikers. According to the manufacturer, it meets standards set forth in the U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers.

In summary, both careful attention to personal hygiene and water treatment have been shown to be important for preventing wilderness diarrhea.

Water disinfection

Two standard textbooks on backcountry medical issues promote water disinfection as a key means of preventing infection. Various commercial water treatment devices are described in detail, and most infectious diarrhea acquired in the U.S. wilderness is considered to be from water-borne pathogens, and effective prevention is therefore thought to require treatment of drinking water as well as proper sanitiation.

Drinking untreated water is something like Russian roulette. Giardia in wilderness water sources may probably not be as prevalent as once believed but it's still present. If a wilderness visitor is confident of untainted alpine water, it's probably safe to drink it untreated, but in areas with significant human or animal activity, treatment is critical in prevention.

Contamination of U.S. backcountry water sources is widespread and disinfection is necessary but exaggerated concern has been raised about the issue. An example is an alleged case where 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

• Wilderness medicine

References

• Backer, Howard D. (2007). "Chapter 61: Field Water Disinfection". In Auerbach, Paul S. ed. (ed.). Wilderness Medicine (5th edition ed.). Philadelphia, PA: Mosby Elsevier. pp. 1368–1417. {{cite book}}: |edition= has extra text (help); |editor= has generic name (help); Cite has empty unknown parameter: |coauthors= (help)