Wilderness-acquired diarrhea

Wilderness diarrhea (WD), also called wilderness-acquired diarrhea 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. A number of researchers in public health and medicine believe the risks of wilderness-acquired diarrhea have been over-stated and are poorly understood by the public (see Controversy section below).

Risk factors for WD include drinking untreated surface water and failure to maintain personal hygiene practices and clean cookware. Most cases of WD are self-limited and the causative agent is most often never known.

Names and definitions

As a variety of TD, WD falls under the more general classification of infectious diarrhea, itself classified (on a physiological basis) as a type of secretory diarrhea. These are all considered forms of gastroenteritis.

Conditions in the wilderness can often mimic those in the developing world, with contaminated water sources and poor sanitation and hygiene, but there are of course important differences. The concept of WD has emerged in the context of relatively affluent North American recreationalists visiting areas that have been set aside as protected areas such as nature reserves or wilderness areas. The concept may easily be extended to similar recreationalists in other developed countries (such as, for example, those in western Europe or Australia). It is less applicable, however, to Western trekkers and other long-term visitors to remote areas of developing countries (such as, for example, Nepal or the highlands of East Africa), because of the very different epidemiologic factors (including distinct pathogens) prevailing there.

The term "backpacker’s diarrhea" might be an appropriate synonym for WD, but that term has traditionally been reserved for a specific cause of much WD — namely giardiasis — and the medical literature is fairly consistent in that usage.

Degree of risk

Rigorous scientific research on the causes and degrees of risk for WD has not been extensive. However, diarrhea has been found to be the most common illness afflicting long-distance hikers in the United States. One recent survey of long-distance hikers on Appalachian Trail by D.R Boulware of the University of Minnesota, found that 45 percent of hikers who consistently treated water suffered from diarrhea, whereas 69% of those who inconsistently treated water experienced it.

Boulware's survey, and a later, similar survey he performed, relied entirely on self-diagnosis and self-reporting by participants, and assumed that the cause of reported illnesses was bacterial infection.

Boulware found that the risk of diarrhea was greater among those who frequently drank untreated water from streams or ponds, whereas practicing "good hygiene" (defined as routine cleaning of cooking utensils and cleaning hands after bowel movements) was associated with a decreased risk. In Boulware's second survey of AT hikers, the role of hygiene was again included, and diarrhea again correlated with the frequency of drinking untreated surface water.

It has been shown that most diarrhea-causing organisms, including Shigella species and Salmonella typhi, hepatitis A virus, and Cryptosporidium species, can survive for weeks to months when frozen in water.

Virologists are in agreement that all surface water supplies in the United States and Canada have the potential to contain naturally occurring human enteroviruses, which are potentially disease-causing.

Causes

In discussing the etiology (causes) of WD, it must be realized that so little research has been specifically directed at diarrhea in a recreational “wilderness” context that it is difficult to distinguish the range of agents causing WD from those causing other types of TD, as well as from those causing water-borne diarrhea where the source of infection is community plumbing or recreational public water such as swimming pools or amusement “water parks”. Nevertheless, one recent authority has presented a frequency distribution of “Enteric Pathogens in U.S. Wildernesses or Recreational Water” as follows. By far the most common causes of diarrhea in this context are the parasites Giardia and Cryptosporidium. Those that are occasionally reported, and have a fair degree of certainly as being the water-borne agent in question, include Campylobacter, hepatitis A virus, hepatitis E virus, enterotoxogenic E. coli, E. coli 0157:H7, Shigella, and various enteric viruses. Agents which may in very unusual circumstances cause diarrhea under these circumstances include Yersinia enterocolitica, Aeromonas hydrophila, and Cyanobacterium.

Symptoms

The onset of WD usually occurs within the first week of return from the field, but may also occur at any time while hiking, particularly if the trip is several days in duration. The incubation period for giardiasis averages about 14 days and that of cryptosporidiosis about 7 days. Certain other bacterial and viral agents generally have shorter incubation periods, although viral hepatitis may take weeks to manifest itself. Most WD cases begin abruptly. The illness usually results in increased frequency, volume, and weight of stool. Altered stool consistency also is common. 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 low or non-existent. Diarrhea is much more serious if there is blood or mucus in the diarrhea, abdominal pain, or high fever. Dehydration is a possibility. Serious, life-threatening illness is rare in the context of WD.

Treatment

WD usually is a self-limited disorder and generally resolves without specific treatment; however, oral rehydration therapy is often beneficial to replace lost fluids and electrolytes. Clear liquids are routinely recommended for adults. Water that is purified is best, along with oral rehydration salts to replenish lost electrolytes. Carbonated water (soda), which has been left out so that the carbonation fizz is gone, is quite useful.

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 antimicrobial therapy. Antibiotics usually are given for 3–5 days, but single dose azithromycin or levofloxacin have been used. If diarrhea persists despite therapy, travelers should be evaluated and treated for possible parasitic infection.

Specific anti-infectives are required to treat bacterial dysentery, for amoebic dysentery, for giardia and for worms. There is no antibiotic effective against Cryptosporidium, which can devastate people with AIDS.

Prevention

Judgments of water safety cannot reliably be made on the basis of the look, smell, and taste of surface water. Conventional guidelines caution that even in the pristine wilderness, surface waters of lakes and streams may be contaminated. Hikers therefore should purify water routinely, avoiding the ingestion of untreated surface water from streams or ponds. It has recently been recognized that the risk of WD can also be reduced by maintaining personal hygiene practices. Specifically, handwashing and cleaning of cookware with both soap and water have been shown to be protective behaviors diminishing diarrhea.

A variety of water disinfection methods that are lightweight, durable and reliable, for the removal of common bacterial and parasitic pathogens, are available commercially (see Portable water purification). The best water-treatment technique to be used by an individual or group in the wilderness depends upon the number of people involved, space and weight considerations, the quality of the available water, personal taste and preferences, and fuel availability. It has been shown that the most significant factor in preventing diarrheal illness in the wilderness is the regularity of water disinfection. Inconsistent use of iodine or chlorine may be due to disagreeable taste, impatience with extended treatment time or excessive treatment complexity due to water temperature and turbidity. For this reason, it has been suggested that for long-distance backpacking, water filtration is a preferred method of disinfection because it is more likely to be persistently and correctly used.

Because methods based on halogens do not kill Cryptosporidium, and because filtration misses some of the viruses, the best protection for all situations may require a two-step process of either filtration or coagulation-flocculation, followed by halogenation. Heat is effective as a one-step process in all situations, but it will not generally improve the palatability of water. 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. The new techniques that use chlorine dioxide, ozone, and UV radiation may prove to be effective one-step techniques, but still require validation in studies.

Controversy

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. [[1]], 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 notes that "misplaced concern" about the safety of wilderness water "have even led to anecdotes about dehydration in recreationalists at high altitude requiring emergent evacuation."

Although Zell says water disinfection is recommended, he 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 might not be cost effective to recommend filtering for recreationalists involved in short-duration trips."

Thomas Welch, a medical doctor and professor at the Tulane School of Public Health's Department of Tropical Medicine, analyzed what he deemed all relevant existing literature and surveyed a majority of state health departments in the United States. Welch concluded that "no studies suggest that North American wilderness waters are a source of bacterial enteritis," and that water filtration and disinfection is generally not necessary in the North American backcountry.

In an editorial for the Wilderness Medical Society Welch was highly critical of studies by D.R. Boulware, which relied on self-reporting and self-diagnosis by backpackers. Welch said Boulware failed to recognize "that infection is only one of the myriad causes of changing bowel habits during or after a trek." (See reference to Boulware's studies in "Risk" section above.) With regard to the risk of diarrhea to backpackers, Welch believes that 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 wrote in his editorial.

Welch's so-called meta-analytic study's initial screening identified 104 articles, nine met the inclusion criteria. Neither of two case reports (detailed report of the diagnosis, treatment, and follow-up of an individual patient) met the criteria of the Centers for Disease Control and Prevention for waterborne disease outbreak. Two studies included data on subjects who were followed forward in time (or "prospective" studies), but neither showed a significant association. Of four studies that included control groups, three reported an odds ratio of greater than one, indicating no relationship between backcountry water and infection.

Robert W. Derlet, a professor at 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 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." Deret adds 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." [[2]]

Derlet says Wilderness water in remote, less-traveled regions of the Sierra is usually free of waterborne pathogens (Giardia lamblia, Cryptosporidium parvum, et al.). Derlet says he routinely drinks untreated water in remote regions but that areas affected by cattle and livestock do present risk. In high-elevation regions of the Sierra, however, "I'd say there is less than a 1 in 100 chance that a person would get sick drinking untreated water from side streams," Derlet says.[[3]]

Derlet says tests that have been done in the Sierra Nevada of California found low levels of coliform bacteria such as Escherichia coli. Many samples showed no coliform bacteria at all; others showed more, especially in areas with cattle gazing or heavy human activity. Derlet, Robert W., James R. Carlson and Mikla N. Noponen (2004), Coliform and Pathologic Bacteria in Sierra Nevada National Forest Wilderness Area Lakes and Streams, Wilderness and Environmental Medicine, V. 15:4, pp 245–249</ref>

Yet another skeptic is Dr. Robert Rockwell, an engineer by training, who has been widely quoted in the press on backcountry water purity, including a feature article in National Geographic Adventure Magazine (Reports of giardia in the wild greatly exaggerated; July 2002).

For nearly 20 years, has made an ongoing review of the scientific literature on this topic pertaining specifically to the Sierra Nevada in California In his carefully documented writings, Rockwell says that "Giardia and other intestinal bugs are for the most part spread by direct fecal-oral or food-borne transmission, not by contaminated drinking water.

Rockwell notes that up to 7 percent of Americans, or up to 1 in 14, are infected with giardiasis, although the majority are asymptomatic. "It is not surprising that wilderness visitors can indeed come home with a case of giardiasis, contracted not from the water...but from one of their friends," Rockwell says.

Among various sources discussed by Rockwell, he cites two surveys of backcountry water in the Sierra Nevada. One survey of 64 sites was completed in 1984 and found giardia concentrations as high as 0.108 cysts per liter and as low as 0.003. A survey completed in 1990 surveyed three sites on ten different dates and found concentrations between 0 and .062 cysts per liter. Rockwell says the San Francisco public water supply on occassion has contained 0.12 cysts per liter, according to data Rockwell cites from the 2000 Annual Water Quality Report published by a local public utilties commission. Using a similar report, Rockwell says the Los Angeles Aqueduct averages 0.03 cysts per liter.

Rockwell says that drinking 89 liters of water with 10 cysts per liter would result in a 50% chance of contracting giardia, with a high probability that any resulting disease would be asymptomatic.

Despite this research, two widely read textbooks on wilderness medicine offer seemingly contradictory viewpoints. Medicine for Mountaineering and Other Wilderness Activities (Seattle, Washington: The Mountaineers Books, 5th edition, 2001), written and reviewed by a team of medical doctors and edited by James Wilkerson, notes that

In recent years, frantic alarms about the perils of giardiasis have aroused exaggerated concern about this infestation. Government agencies, particularly the U.S. Park Service and the National Forest Service, 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.

Yet the same work also contains a chapter (on “Immunizations, Sanitation and Water Disinfection”) by another author offering the following different observation:

In recent years, widespread microbial contamination of backcountry water sources in the United States has been recognized. The single cell parasite Cryptosporidium is essentially ubiquitous, and its universal presence has dictated changes in water disinfection techniques previously considered completely effective.

Thus two authors in the same widely used textbook convey countervailing opinions on the safety of backcountry water.

Another widely used textbook, Wilderness Medicine, edited by Paul S. Auerbach, considers drinking untreated water in the wilderness unsafe, and advises water disinfection while describing various commercial water treatment devices in detail. The most recent (2007) edition of Auerbach’s Wilderness Medicine maintains:

The majority of pathogens that cause traveler’s diarrhea or wilderness-acquired diarrhea can be either food-borne or water borne; however, waterborne pathogens from drinking untreated surface water or from an inadvertent ingestion during water recreational activity probably account for most infectious diarrhea acquired in the U.S. wilderness. Avoidance of all these pathogens requires proper sanitation and water disinfection.

See also

• Wilderness medicine