Traveler's diarrhea

Traveler's diarrhea (TD) is the most common illness affecting travelers.^[1] An estimated 10 million people—20% to 50% of international travelers—develop it annually.^[2] TD is defined as three or more unformed stools in 24 hours passed by a traveler, commonly accompanied by abdominal cramps, nausea, and bloating.^[3] Its diagnosis does not imply a specific organism, but enterotoxigenic Escherichia coli is the most commonly isolated pathogen.^[4] Most cases are self-limited; treatment is not routinely prescribed nor the pathogen identified unless symptoms become severe or persistent.

Signs and symptoms

The onset of TD usually occurs within the first week of travel, but may occur at any time while traveling, and even after returning home. When it appears depends in part on the specific infectious agent. 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. Most TD cases begin abruptly.

Typically, a traveler experiences four to five loose or watery bowel movements each day. Other commonly associated symptoms are diarrhea, abdominal cramping, bloating, low fever, urgency, disability to hold the feces and malaise,^[2] and appetite is usually low or nonexistent.^[3]

Blood or mucus in the diarrhea, abdominal pain, or high fever heralds a more serious cause, such as cholera, characterized by a rapid onset of symptoms including weakness, malaise, and torrents of watery diarrhea with flecks of mucus (described as "rice water" stools). Dehydration is a serious consequence of cholera; death may (rarely) occur as quickly as 24 hours after onset.^[3]

Causes

Infectious agents are the primary cause of travelers' diarrhea. Bacterial enteropathogens cause approximately 80% of cases. Viruses and protozoans account for most of the rest.^[2]

The most common causative agent isolated in countries surveyed has been enterotoxigenic Escherichia coli (ETEC).^[2] Enteroaggregative E. coli is increasingly recognized and many studies do not look for this important bacterium.^[3] Shigella spp. and Salmonella spp. are other common bacterial pathogens. Campylobacter, Yersinia, Aeromonas, and Plesiomonas spp. are less frequently found. Some bacteria release toxins which bind to the intestinal wall and cause diarrhea; others damage the intestines themselves by their direct presence.

While viruses are associated with less than 20% of adult cases of traveler's diarrhea, they may be responsible for nearly 70% of cases in infants and children. Diarrhea due to viral agents is unaffected by antibiotic therapy, but is usually self-limited.^[3] Protozoans such as Giardia lamblia and Cryptosporidium can also cause diarrhea.

Pathogens implicated in travelers' diarrhea appear in the table at right.^[3]

A sub-type of traveler's diarrhea afflicting hikers and campers, sometimes known as wilderness diarrhea, may have a somewhat different frequency distribution of pathogens.^{[citation needed]}

Risk factors

The primary source of infection is ingestion of fecally-contaminated food or water. Attack rates are similar for men and women.^[2]

The most important determinant of risk is the traveler's destination. High risk destinations include developing countries in Latin America, Africa, the Middle East, and Asia.^[2] Among backpackers, additional risk factors include drinking untreated surface water and failure to maintain personal hygiene practices and clean cookware.^[5] Campsites often have very primitive (if any) sanitation facilities, making them potentially as dangerous as any developing country.

Although traveler's diarrhea usually resolves within three to five days (mean duration: 3.6 days), in about 20% of cases the illness is severe enough to require bedrest, and in 10% the illness duration exceeds one week.^[3] For those prone to serious infections, such as bacillary dysentery, amoebic dysentery, and cholera, TD can occasionally be life-threatening.^[3] Others at higher-than-average risk include young adults, immunosuppressed persons, persons with inflammatory bowel disease or diabetes, and those taking H2 blockers or antacids.^[2]

Immunity

Travelers often get diarrhea from eating and drinking foods and beverages that have no adverse effects on local residents. This is due to immunity that develops with constant, repeated exposure to pathogenic organisms. The extent and duration of exposure necessary to acquire immunity has not been determined; it may vary with each individual organism. However, a study among expatriates in Nepal suggests that immunity may take up to seven years to develop—presumably in adults who avoid deliberate pathogen exposure.^[6] Conversely, immunity that American students acquired while living in Mexico disappeared, in one study, as quickly as 8 weeks after cessation of exposure.^[7]

Prevention

The best means of prevention is to avoid any questionable foods or beverages. Traveler's diarrhea is fundamentally a sanitation failure, leading to bacterial contamination of drinking water and food. It is best prevented through proper water quality management systems, as found in responsible hotels and resorts. In the absence of that, the next best option for travelers is to take individual precautions:

• Drink safe beverages, which include bottled water, bottled carbonated beverages, hot tea or coffee, and water boiled or appropriately treated by the traveler.^[3] Caution should be exercised with hot beverages, which may be only heated, not boiled.
• Maintain good hygiene and only use safe water for drinking and tooth brushing.^[3]
• Avoid ice, which may not have been made with bottled water.
• In restaurants, insist that bottled water be unsealed in your presence. Reports of locals filling empty bottles with untreated tap water and reselling them as purified water have surfaced.^[3] When in doubt, a bottled carbonated beverage is the safest choice, since it is difficult to carbonate water when refilling a used bottle.
• Avoid eating raw fruits and vegetables unless the traveler peels them personally.^[2]
• Avoid green salads, because it is unlikely that the lettuce will have been washed with bottled water.^[2]

If handled properly, well-cooked and packaged foods are usually safe.^[2] Eating raw or undercooked meat and seafood should be avoided. Unpasteurized milk, dairy products, mayonnaise and pastry icing are associated with increased risk for TD, as are foods or drinking beverages purchased from street vendors or other establishments where unhygienic conditions may be present.^[3]

Travelers can treat their own water if necessary, although the wide availability of safe bottled water makes these interventions unnecessary for all but the most remote destinations.^[3] Techniques include boiling, filtering, chemical treatment, and ultraviolet light. Boiling kills all bacteria and viruses immediately. (It is not necessary to keep it at a boil for any length of time.^[8] All microorganisms are killed within seconds as the temperature passes 55-70 C.) Filters eliminate some microogranisms, but not viruses. Chemical treatment can be done with halogens, which can be in the form of chlorine bleach (2 drops per litre), tincture of iodine (5 drops per litre), or tablets. Halogens are not effective against protozoan cysts such as giardia. An ultraviolet (UV) water purification device is available commercially that allows treatment of small amounts of water at room temperature. The UV light bonds DNA thymine rings, preventing the survival or replication of any infectious organisms in the water. It kills both viruses and cellular organisms. Other claimed advantages include no taste alteration, elimination of need for boiling, and decreased long-term cost compared with bottled water.

Other preventive measures include over-the-counter anti-diarrhea products and in certain situations, prophylactic medications and supplements. Studies show a decrease in the incidence of TD with use of bismuth subsalicylate and antimicrobial chemoprophylaxis.^[3]

Bismuth subsalicylate (two tablets or two ounces four times daily) will reduce the likelihood of travelers' diarrhea, but few travelers adhere to a four-times-per-day regimen because it is inconvenient.^[9] Side effects may include black tongue, black stools, nausea, constipation, and ringing in the ears (tinnitus). Bismuth subsalicylate should not be taken by those with aspirin allergy, kidney disease, or gout, nor concurrently with certain antibiotics, and should not be taken for more than three weeks.^[9]

Though effective, antibiotics are not recommended in most situations to prevent diarrhea before it occurs, because of the risk of adverse reactions to the antibiotics, and because intake of prophylactic antibiotics may decrease effectiveness of such drugs should a serious infection occur. Antibiotics can also cause vaginal yeast infections (which many women consider a worse problem than the diarrhea^[9]). Also, antibiotics can cause a disease called pseudomembranous colitis which results in severe, unrelenting diarrhea.^[10]

However, prophylaxis may be warranted in special situations where benefits outweigh the above risks, such as immunocompromised travelers, chronic intestinal disorders, prior history of repeated disabling bouts of traveler's diarrhea, or scenarios in which onset of diarrhea might prove particularly troublesome. Options for prophylactic treatment include the quinolone antibiotics (norfloxacin, ciprofloxacin, ofloxacin, among others), and trimethoprim/sulfamethoxazole. Quinolone antibiotics may bind to metallic cations such as bismuth, and should not be taken concurrently with bismuth subsalicylate. Trimethoprim/sulfamethoxazole should not be taken by anyone with a history of sulfa allergy.^[9]

A few pathogen-specific vaccines have become available, and others are under development. Dukoral, an oral vaccine against Vibrio cholerae, has demonstrated up to 43% protective efficacy against TD when one dose is given a few weeks before travel and a second a week before travel, although it is not officially approved for that indication in most countries.^[11] Several vaccine candidates targeting enterotoxigenic E. coli (ETEC) and Shigella are in various stages of development.^[12][13]

Two probiotics (Saccharomyces boulardii and a mixture of Lactobacillus acidophilus and Bifidobacterium bifidum) have been studied as a treatment for TD. In a meta-analysis by McFarland (2005), no serious adverse reactions were reported in 12 trials. These probiotics may offer a safe and effective method to prevent TD, but due to strain stability and survivability issues, they may not always be an appropriate choice.^[14] Prebiotics, as an alternative, are more stable than probiotics during passage through the upper gastrointestinal tract and are able to induce antimicrobial effects principally through their selective stimulation of our own beneficial gut bacteria. However, prebiotics act mainly in the large intestine, while the infective organisms causing TD act in the small intestine. Therefore, current prebiotics (such as fructooligosaccharide) have very limited application as preventative agents. Second generation prebiotic galactooligosaccharides, such as B-GOS (Bimuno), have additional properties such as positive effect on immunity^[15] and direct interaction with the host gut epithelium, preventing the attachment and invasion of gastrointestinal pathogens.^[16] B-GOS was shown to result in significant reduction in the incidence and duration of TD in a study with human volunteers travelling to countries with medium to high risk of developing TD.^[17]

Treatment

Most cases of TD are mild and resolve in a few days without treatment with antibiotics or antimotility drugs. Severe or protracted cases, however, may result in significant fluid loss and dangerous electrolytic imbalance. Adequate fluid intake (oral rehydration therapy) is essential to replace lost fluids and electrolytes. Clear, disinfected water or other liquids are routinely recommended for adults.^[2] 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 useful if nothing else is available.^[3] In severe or protracted cases, the oversight of a medical professional is advised.

Antibiotics

If diarrhea becomes severe (typically defined as three or more loose stools in a 24-hour period)—or if diarrhea is bloody, or fever occurs with shaking chills, or abdominal pain becomes marked, or diarrhea persists for more than 72 hours—medical treatment should be sought. Such patients may benefit from antimicrobial therapy.^[2] Antibiotics are typically given for three to five days,^[2] but single doses of azithromycin or levofloxacin have been used.^[18] If diarrhea persists despite therapy, travelers should be evaluated for possible viral or parasitic infections,^[2] bacterial or amoebic dysentery, Giardia, helminths, or cholera.^[3]

A systematic review found that antibiotic treatment in Travelers diarrhea is associated with a shorter duration and lesser severity of diarrhea but with a higher incidence of side-effects.^[19]

Antimotility agents

Antimotility drugs such as loperamide and diphenoxylate reduce the symptoms of diarrhea by slowing transit time in the gut. They should be taken as necessary to slow the frequency of stools, but not enough to stop bowel movements completely, which delays expulsion of the causative organisms from the intestines.^[2] Adverse reactions may include nausea, vomiting, abdominal pain, hives or rash, and loss of appetite.^[20] Antimotility agents should not, as a rule, be given to children under age two.^[9]

Epidemiology

Each year 20%–50% of international travelers (more than 10 million people) develop traveler's diarrhea.^[2] It is more common in the developing world, where rates exceed 60%, than in developed countries.^[21]

Society and culture

There are a number of colloquialisms for travelers' diarrhea contracted in various localities, such as "Montezuma's revenge", "turistas",^[22] or "Aztec two step" in Mexico; and "Pharaoh's Revenge," "mummy's tummy," or "Cairo two-step" in Egypt. Many other colorful synonyms exist in other regions of the world, some of which have found their way into the arts and literature. For example, Aamir Khan titled his 2011 Hindi film Delhi Belly, after the popular Indian colloquialism. In the United States, euphemisms such as "Hershey squirts," "the runs," and "the McShits" are commonplace.

Montezuma's revenge

Montezuma's revenge (var. Moctezuma's revenge) is the colloquial term for any cases of traveler's diarrhea contracted by tourists visiting Mexico. The name refers to Moctezuma II (1466–1520), the Tlatoani (ruler) of the Aztec civilization who was defeated by Hernán Cortés, the Spanish conquistador.

Wilderness diarrhea

Wilderness diarrhea (WD), also called wilderness-acquired diarrhea (WAD) or backcountry diarrhea, refers to diarrhea among backpackers, hikers, campers and other outdoor recreationalists that appears in wilderness or "backcountry" situations, either at home or abroad.^[23] It is due to the same agents as all other traveler's diarrhea, which are usually bacterial and viral and caused by hand-to-mouth contamination by fecal microorganisms. Since wilderness campsites seldom provide access to sanitation facilities, the infection risk is similar to that of any developing country.^[5] The most important preventative measure is to practice good toilet hygiene.^[24] It may also be helpful to avoid sharing cooking pots.

Wilderness diarrhea is less likely to be caused by contaminated water sources. Starting in the 1970s, it began to be widely believed that giardiasis was prevalent even in seemingly pristine water, but in fact a 2000 epidemiological study found that "the evidence for an association between drinking backcountry water and acquiring giardiasis is minimal."^[25] In many wilderness areas, such as the Sierra Nevada mountains, water taken from streams has fewer giardia cysts than municipal tap water.^[26] Giardia is often asymptomatic, and is extremely common among the general population, with about one third of toddlers in the US being infected. The incubation period is about a week, so any symptomatic infection occurring during a weekend backpacking trip would have to have been acquired before the trip.^[23]

References

Wikivoyage has a travel guide for Travellers' diarrhea.

 This article incorporates public domain material from websites or documents of the Centers for Disease Control and Prevention.