Potability of backcountry water
Encyclopedia
Wilderness acquired diarrhea (WAD), wilderness-acquired diarrhea, wilderness diarrhea, or backcountry diarrhea, is diarrhea
that is caused by pathogens that have infected
people when they were in the wilderness
. It is a much-discussed hazard among backpackers, hikers, campers and other outdoor recreationalists who visit remote areas of the developed world. Risk factors include insufficient washing of hands and food utensils and, to a lesser extent, drinking untreated surface water. Cases of WAD tend to be self-limited and the specific cause (microbe) is most often never known. Based on both systematic and less formal reviews of epidemiologic data and literature, various medical
and public health
researchers who have studied the topic believe that the risks of WAD have been over-stated and are poorly understood by the public.
, 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 the different pathogens that are most likely to cause infection.
, viruses, and parasites (protozoa
). The most commonly reported are the protozoa Giardia and Cryptosporidium. Other infectious agents may play a larger role than generally believed and include Campylobacter
, hepatitis A virus, hepatitis E virus
, enterotoxogenic E. coli, e. coli 0157:H7, Shigella
, and various other viruses. More rarely, Yersinia enterocolitica
, Aeromonas hydrophila
, and Cyanobacterium may also cause disease.
Giardia lamblia
does not tolerate freezing but 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
may 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.
Modes of acquiring infection from these causes are limited to fecal-oral transmission, and contaminated water and food. The major factor governing pathogen content of surface water is human and animal activity in the watershed. The risk of WAD from untreated water may have been over-stated relative to the risk from insufficient hygiene
.
s for giardiasis
and cryptosporidiosis
are each 7 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 resulting from WAD is extremely rare but can occur in people with weakened immune systems.
Some people may be carriers and not exhibit symptoms.
A suspected case of wilderness acquired diarrhea may be assessed within the general context of intestinal complaints. During any given four-week period, as many as 7.2% of Americans may experience some form of infectious or non-infectious diarrhea. There are an estimated 99 million annual cases of intestinal infectious disease in the United States, most commonly from viruses, followed by bacteria and parasites, including Giardia and Cryptosporidium. Giardia alone may infect up to 10% of Americans at any one time. However, because most carriers are asymptomatic, there are only an estimated 2 million U.S. cases of symptomatic giardiasis annually spread mostly by fecal-oral or food-borne transmission.
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 stool
s — should be treated by a doctor and may benefit from antibiotics, usually given for 3–5 days. Alternatively, a single dose azithromycin
or levofloxacin
may be prescribed. If diarrhea persists despite therapy, travelers should be evaluated and treated for possible parasitic infection.
Cryptosporidium can be quite dangerous to patients with compromised immune systems. Alinia (nitazoxanide) is approved by the FDA for treatment of Cryptosporidium.
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.
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. Some hikers use small portable UV devices which meet the U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers, for example, the SteriPEN. Another approach to portable UV water purification is solar disinfection which is called SODIS. Clear water is sterilized by putting it in a clear polyethylene (PET
) bottle and leaving it in direct sunlight for 6 hours.
Rain storms can either improve or worsen water quality. They can wash contaminants into water and stir up contaminated sediments with increasing flow, but can also dilute contaminants by adding large amounts of water.
Unfortunately, there have not been any epidemiological studies to validate the above, except possibly for the case of spring water.
s may reduce the incidence of diarrhea.
s 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.
s and cattle pastures.
Most surveys of backcountry water in the United States have found very low or no Giardia cysts. However, very few studies have addressed the issue of transient contamination. According to one researcher, the likely model for the risk of Giardia from wilderness water is pulse contamination, that is, a brief period of high cyst concentration from fecal contamination.
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
that is caused by pathogens that have infected
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
people when they were in the wilderness
Wilderness
Wilderness or wildland is a natural environment on Earth that has not been significantly modified by human activity. It may also be defined as: "The most intact, undisturbed wild natural areas left on our planet—those last truly wild places that humans do not control and have not developed with...
. It is a much-discussed hazard among backpackers, hikers, campers and other outdoor recreationalists who visit remote areas of the developed world. Risk factors include insufficient washing of hands and food utensils and, to a lesser extent, drinking untreated surface water. Cases of WAD tend to be self-limited and the specific cause (microbe) is most often never known. Based on both systematic and less formal reviews of epidemiologic data and literature, various medical
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
and public health
Public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...
researchers who have studied the topic believe that the risks of WAD have been over-stated and are poorly understood by the public.
Names and definitions
Diarrhea acquired in the wilderness or other remote areas is typically a form of infectious diarrheaInfectious diarrhea
Infectious diarrhea or Contagious diarrhea may be defined as diarrhea caused by an infection of the digestive system by a bacterium, virus, or parasite that results in frequent bowel motions producing excessive amounts of liquidy feces.-Causes:...
, itself classified as a type of secretory diarrhea. These are all considered forms of gastroenteritis
Gastroenteritis
Gastroenteritis is marked by severe inflammation of the gastrointestinal tract involving both the stomach and small intestine resulting in acute diarrhea and vomiting. It can be transferred by contact with contaminated food and water...
. 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 the different pathogens that are most likely to cause infection.
Causes
Infectious diarrhea acquired in the wilderness is caused by various bacteriaBacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, viruses, and parasites (protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
). The most commonly reported are the protozoa Giardia and Cryptosporidium. Other infectious agents may play a larger role than generally believed and include Campylobacter
Campylobacter
Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...
, hepatitis A virus, hepatitis E virus
Hepatitis E virus
Hepatitis E virus is the infective organism that causes hepatitis E.The viral particles are 27 to 34 nanometers in diameter, are non-enveloped and contain a single-strand of positive-sense RNA that is approximately 7300 bases in length. The virus particle was first visualised in 1983 but was only...
, enterotoxogenic E. coli, e. coli 0157:H7, Shigella
Shigella
Shigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...
, and various other viruses. More rarely, Yersinia enterocolitica
Yersinia enterocolitica
Yersinia enterocolitica is a species of gram-negative coccobacillus-shaped bacterium, belonging to the family Enterobacteriaceae. Yersinia enterocolitica infection causes the disease yersiniosis, which is a zoonotic disease occurring in humans as well as a wide array of animals such as cattle,...
, Aeromonas hydrophila
Aeromonas hydrophila
Aeromonas hydrophila is a heterotrophic, Gram-negative, rod shaped bacterium, mainly found in areas with a warm climate. This bacterium can also be found in fresh, salt, marine, estuarine, chlorinated, and un-chlorinated water. Aeromonas hydrophila can survive in aerobic and anaerobic...
, and Cyanobacterium may also cause disease.
Giardia lamblia
Giardia lamblia
Giardia lamblia is a flagellated protozoan parasite that colonizes and reproduces in the small intestine, causing giardiasis. The giardia parasite attaches to the epithelium by a ventral adhesive disc, and reproduces via binary fission...
does not tolerate freezing but 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
Cryptosporidium
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhea in humans.Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea...
may 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
Shigella
Shigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...
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.
Modes of acquiring infection from these causes are limited to fecal-oral transmission, and contaminated water and food. The major factor governing pathogen content of surface water is human and animal activity in the watershed. The risk of WAD from untreated water may have been over-stated relative to the risk from insufficient hygiene
Hygiene
Hygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...
.
Symptoms
The average incubation periodIncubation period
Incubation period is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent...
s for giardiasis
Giardiasis
Giardiasis or beaver fever in humans is a diarrheal infection of the small intestine by a single-celled organism Giardia lamblia. Giardiasis occurs worldwide with a prevalence of 20–30% in developing countries. In the U.S., 20,000 cases are reported to the CDC annually, but the true annual...
and cryptosporidiosis
Cryptosporidiosis
Cryptosporidiosis, also known as crypto, is a parasitic disease caused by Cryptosporidium, a protozoan parasite in the phylum Apicomplexa. It affects the intestines of mammals and is typically an acute short-term infection...
are each 7 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
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
in stools, abdominal pain, or high fever. Dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
is a possibility. Life-threatening illness resulting from WAD is extremely rare but can occur in people with weakened immune systems.
Some people may be carriers and not exhibit symptoms.
Diagnosis
It may be difficult to associate a particular case of diarrhea with a recent wilderness trip of a few days because incubation of the disease may outlast the trip. Studies of trips that are much longer than the average incubation period, e.g. a week for Cryptosporidium and Giardia, are less susceptible to these errors since there is enough time for the diarrhea to occur during the trip. Other bacterial and viral agents have shorter incubation periods, although hepatitis may require weeks.A suspected case of wilderness acquired diarrhea may be assessed within the general context of intestinal complaints. During any given four-week period, as many as 7.2% of Americans may experience some form of infectious or non-infectious diarrhea. There are an estimated 99 million annual cases of intestinal infectious disease in the United States, most commonly from viruses, followed by bacteria and parasites, including Giardia and Cryptosporidium. Giardia alone may infect up to 10% of Americans at any one time. However, because most carriers are asymptomatic, there are only an estimated 2 million U.S. cases of symptomatic giardiasis annually spread mostly by fecal-oral or food-borne transmission.
Treatment
WAD is typically self-limited, generally resolving without specific treatment. Oral rehydration therapyOral rehydration therapy
Oral rehydration therapy is a simple treatment for dehydration associated with diarrhoea, particularly gastroenteritis or gastroenteropathy, such as that caused by cholera or rotavirus. ORT consists of a solution of salts and sugars which is taken by mouth...
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
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
, abdominal cramps, fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, or blood in stool
Blood in stool
In medicine, when referring to human feces, blood in stool can refer to multiple conditions:* Melena, with more blackish appearance, originating in upper parts of the gastrointestinal tract...
s — should be treated by a doctor and may benefit from antibiotics, usually given for 3–5 days. Alternatively, a single dose azithromycin
Azithromycin
Azithromycin is an azalide, a subclass of macrolide antibiotics. Azithromycin is one of the world's best-selling antibiotics...
or levofloxacin
Levofloxacin
Levofloxacin is a synthetic chemotherapeutic antibiotic of the fluoroquinolone drug class and is used to treat severe or life-threatening bacterial infections or bacterial infections that have failed to respond to other antibiotic classes. It is sold under various brand names, such as Levaquin and...
may be prescribed. If diarrhea persists despite therapy, travelers should be evaluated and treated for possible parasitic infection.
Cryptosporidium can be quite dangerous to patients with compromised immune systems. Alinia (nitazoxanide) is approved by the FDA for treatment of Cryptosporidium.
Prevention
Since wilderness acquired diarrhea can be caused by insufficient hygiene, contaminated water, and (possibly) increased susceptibility from vitamin deficiency, prevention methods should address these causes.Hygiene
The risk of fecal-oral transmission of pathogens that cause diarrhea can be significantly reduced by good hygiene, including washing hands with soap and water after urination and defecation, and washing eating utensils with warm soapy water. Additionally a three-bowl system can be used for washing eating utensils.Treating water
Water can be treated in the wilderness through filtering, chemical disinfectants, a portable ultraviolet light device, pasteurizing or boiling. Factors in choice may include the number of people involved, space and weight considerations, the quality of available water, personal taste and preferences, and fuel availability.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
Flocculation
Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...
, followed by halogenation
Halogenation
Halogenation is a chemical reaction that incorporates a halogen atom into a molecule in substitution of hydrogen atom. Halogenation takes place in the gas phase. There are four types of halogenation: fluorination, chlorination, bromination, and iodination...
. Boiling is effective in all situations.
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. Some hikers use small portable UV devices which meet the U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers, for example, the SteriPEN. Another approach to portable UV water purification is solar disinfection which is called SODIS. Clear water is sterilized by putting it in a clear polyethylene (PET
Polyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...
) bottle and leaving it in direct sunlight for 6 hours.
Water risk avoidance
Different types of water sources may have different levels of contamination:- More contamination may be in water that
- likely could have passed through an area subject to heavy human or animal use
- is cloudy, has surface foam, or has some other suspicious appearance.
- Less contamination may be in water from
- springs (provided the true source is not surface water a short distance above)
- large streams (those entering from the side may have less contamination than those paralleling the trail)
- fast-flowing streams
- higher elevations
- lakes with undisturbed sediments (10 days undisturbed water storage can result in 75-99% removal of coliform bacteriaColiform bacteriaColiform bacteria are a commonly used bacterial indicator of sanitary quality of foods and water. They are defined as rod-shaped Gram-negative non-spore forming bacteria which can ferment lactose with the production of acid and gas when incubated at 35-37°C...
by settling to the bottom) - freshly melted snow
- deep wells (provided they aren't subject to contamination from surface runoff)
- regions where there was a heavy snow year when streams run full and long compared to dry years.
Rain storms can either improve or worsen water quality. They can wash contaminants into water and stir up contaminated sediments with increasing flow, but can also dilute contaminants by adding large amounts of water.
Unfortunately, there have not been any epidemiological studies to validate the above, except possibly for the case of spring water.
Vitamins
One study suggests that on very long trips in the wilderness, taking multivitaminMultivitamin
A multivitamin is a preparation intended to supplement a human diet with vitamins, dietary minerals, and other nutritional elements. Such preparations are available in the form of tablets, capsules, pastilles, powders, liquids, and injectable formulations...
s may reduce the incidence of diarrhea.
Epidemiology
The risk of acquiring infectious diarrhea in the wilderness arises from inadvertent ingestion of pathogens. Various studies have sought to estimate diarrhea attack rateAttack rate
In epidemiology, an attack rate is the cumulative incidence of infection in a group of people observed over a period of time during an epidemic, usually in relation to foodborne illness....
s 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
National Outdoor Leadership School
The National Outdoor Leadership School , is a non-profit outdoor education school based in the United States dedicated to teaching environmental ethics, technical outdoor skills, safety and judgment, and leadership on extended wilderness expeditions...
(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
Appalachian Trail
The Appalachian National Scenic Trail, generally known as the Appalachian Trail or simply the AT, is a marked hiking trail in the eastern United States extending between Springer Mountain in Georgia and Mount Katahdin in Maine. It is approximately long...
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
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
. A study at Grand Teton National Park found 69% of diarrhea affected visitors had no identifiable cause, that 23% had diarrhea due to Campylobacter
Campylobacter
Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...
and 8% of patients with diarrhea had giardiasis
Giardiasis
Giardiasis or beaver fever in humans is a diarrheal infection of the small intestine by a single-celled organism Giardia lamblia. Giardiasis occurs worldwide with a prevalence of 20–30% in developing countries. In the U.S., 20,000 cases are reported to the CDC annually, but the true annual...
. 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.
Backcountry water quality surveys
Infection by fecal coliform bacteria, which indicate fecal pollution, represent a much higher risk than giardiasis. Risks are highest in surface water near trails used by pack animalPack animal
A pack animal or beast of burden is a working animal used by humans as means of transporting materials by attaching them so their weight bears on the animal's back; the term may be applied to either an individual animal or a species so employed...
s and cattle pastures.
Most surveys of backcountry water in the United States have found very low or no Giardia cysts. However, very few studies have addressed the issue of transient contamination. According to one researcher, the likely model for the risk of Giardia from wilderness water is pulse contamination, that is, a brief period of high cyst concentration from fecal contamination.