Traveler's Diarrhea : Prevention and Self-Treatment

Traveler's diarrhea is a common malady affecting up to 60% of international travelers during a 2-week trip. Areas of the world can be divided into high, intermediate, and low risk for acquiring traveler's diarrhea ( Fig. 8.1 ). Lowering risk from high to intermediate speaks to excellent efforts by many countries to improve their food and beverage hygiene. However, in the preparation of travelers for self-treatment or prophylaxis of traveler's diarrhea, intermediate risk is managed practically as if the risk were high. Traveler's diarrhea is usually a self-limited illness consisting of 4-6 days of loose stools, sometimes accompanied by low-grade fever, nausea, abdominal cramping, headache, and/or general malaise. Up to 25% of sufferers will alter their activities, 15% will be confined to bed, and 1% will be hospitalized.

Classic traveler's diarrhea occurs when immunologically naïve persons move from industrialized nations to developing areas of the world. Travelers moving in the opposite direction experience far less illness. While travelers might experience gastrointestinal (GI) upset after exposure to new foods and spices, classic traveler's diarrhea is caused by microorganisms contaminating food and, to a much lesser extent, beverages. Other risk factors have been elucidated, but most are either inherent to the chosen itinerary or are host factors that are not amenable to modification ( Table 8.1 ).

TABLE 8.1

Risk Factors for Traveler's Diarrhea

Risk Factor	Comments
Age	Highest in infants and young adults
Source of food and water	Quality may depend on type of travel, adherence to dietary precautions
Type of travel	Adventurous travelers, prolonged stays
Decreased gastric acidity	Acid-reducing medications, achlorhydria, hypochlorhydria, gastrectomy
Immune deficiency	HIV infection with low CD4 count; IgA deficiency
Blood group O	Increased risk of severe disease with Vibrio cholerae El Tor

HIV, Human immunodeficiency disease; IgA, immunoglobulin A.

Enteropathogens associated with traveler's diarrhea include bacteria, viruses, and parasites. A majority of cases of the syndrome are caused by bacteria, which explains the success of antibiotics in treatment and prevention. Pre-travel vaccinations against enteropathogens can protect against typhoid (a rare cause of traveler's diarrhea), cholera (rare among tourists and business travelers), and hepatitis A (not classically included as a cause of traveler's diarrhea, since it does not always cause loose stools). A degree of cross protection against common enterotoxigenic Escherichia coli can be achieved with oral cholera vaccine; however, protection is modest, requires two doses completed prior to travel, and does not provide enough protection against other causes of traveler's diarrhea to obviate preparing the traveler for self-treatment and prophylaxis. The immune protection afforded by vaccination and natural protective mechanisms of the GI tract (mainly gastric acidity) can be overwhelmed by the ingestion of heavily contaminated food or water. Some pathogens such as Shigella can cause disease after ingestion of a relatively low infectious inoculum.

Common-sense food and water precautions during travel should guard against contracting traveler's diarrhea. However, contamination is ubiquitous in developing countries, and many travelers simply do not exercise the stringent precautions required to prevent disease. Despite efforts in travel medicine clinics to educate clientele about food and water hygiene, risk remains high among most travelers to high-risk areas of the world. For this reason a primary goal during a pre-travel clinic visit is to prepare the traveler for self-treatment and sometimes to prescribe chemoprophylaxis.

Etiology

Bacteria are responsible for the majority of cases of traveler's diarrhea, with viruses and parasites accounting for significantly lower numbers; however, the ratios depend somewhat on the geographic region, time of year, and presence of local outbreaks (e.g., norovirus and diarrhea aboard a cruise ship). In many cases of traveler's diarrhea, no etiologic agent can be identified unless a research laboratory is engaged. While clinical presentation does not usually predict the pathogen that will be isolated, occasionally, bloody or mucoid stools and high fever signal dysentery caused by one of the invasive pathogens.

Enterotoxigenic strains of E. coli (ETEC) bacteria are the most common identifiable cause of acute diarrhea in travelers visiting developing and tropical countries, with the exception of Southeast Asia, where Campylobacter is the most prevalent organism, followed closely by ETEC. The heat-labile toxin of ETEC is similar to cholera toxin; it causes prolonged secretion of isotonic fluid containing high amounts of bicarbonate and potassium throughout all segments of the small bowel via stimulation of adenylate cyclase. Oral cholera vaccine elicits antibodies to the B subunit of cholera toxin that cross-react with the heat-labile toxin of ETEC, and this is the basis for the vaccine's partial protection against traveler's diarrhea. The heat-stable toxin alters fluid transport via stimulation of guanylate cyclase in the jejunum and ileum only. Many ETEC strains produce both toxins.

Campylobacter species, mostly C. jejuni , are common etiologic agents of traveler's diarrhea, especially in Southeast Asia, but are less frequently isolated in many other regions of the world. Seasonal variance occurs in rates of Campylobacter infections: peak incidence in the United States or United Kingdom occurs in the summer or spring, whereas in North Africa it peaks during the drier winter months.

Other bacterial enteric pathogens less frequently isolated in cases of traveler's diarrhea include species of Salmonella , Shigella , Aeromonas , Plesiomonas shigelloides , Vibrio cholerae , V. parahaemolyticus , V. vulnificus , and Yersinia enterocolitica .

Norovirus, implicated in outbreaks of food-borne gastroenteritis, is a common cause of gastroenteritis in adults and accounts for as high as 10-15% of the cases of traveler's diarrhea in some studies. Rotavirus is less common among adult travelers. Infections with hepatitis A virus or hepatitis E virus can account for some cases of traveler's diarrhea.

The parasites causing acute diarrhea in travelers are usually protozoans, including Giardia lamblia , Cryptosporidium sp., Cyclospora cayetanensis , Entamoeba histolytica , Isospora belli , and Dientamoeba fragilis . Although less common, helminthic infections can also account for diarrhea in travelers.

Food, fish, and shellfish poisoning ( Chapters 33 and 34) can also be included among occasional to rare causes of acute diarrhea in travelers.

Prevention of Traveler's Diarrhea

Potential preventive strategies for traveler's diarrhea include dietary precautions, appropriate immunizations, and chemoprophylactic agents.

Dietary Precautions

Adherence to advice on food and water precautions should logically reduce the risk from all forms of traveler's diarrhea ( Table 8.2 ). Most travelers to urban destinations and tourist attractions do not need to learn techniques for water purification ( Chapter 7 ); clean, bottled water is readily available for most travelers around the world. However, adherence to principles of food and beverage hygiene is difficult to sustain for most, particularly longer-term or adventurous, travelers. Families with small infants should consider keeping young infants off the ground and maintaining breast feeding during the trip.

TABLE 8.2

Ten Tips for Selection of Safe Food and Water

1.
Drink purified, bottled water or carbonated beverages.
2.
Eat foods that are thoroughly cooked and served piping hot.
3.
Eat fruits that have thick skins (they should be peeled at the table by the traveler).
4.
Avoid salads made with raw vegetables, especially leafy green vegetables.
5.
Do not use ice cubes, even in beverages containing alcohol.
6.
Eat and drink dairy products made only from pasteurized milk.
7.
Avoid shellfish and raw or undercooked seafood, even if “preserved” or pickled with vinegar or the juice of lemon or lime.
8.
Do not buy and eat food sold by street vendors.
9.
If canned beverages are cooled by submersion of the can in a bucket of ice water or in a stream, dry off the outside of the container before drinking the contents.
10.
Use purified water for brushing teeth and for taking medications.

Immunizations

Oral cholera vaccines are only modestly effective against ETEC strains and are not readily available worldwide. Vaccines against hepatitis A and typhoid are effective, but these pathogens account for very few cases of traveler's diarrhea. No vaccines are currently available to prevent the many remaining causes of traveler's diarrhea.

Chemoprophylaxis

Medications that can be used to prevent traveler's diarrhea are shown in Table 8.3 .

TABLE 8.3

Drug Regimens for Prevention of Traveler's Diarrhea

Drug ^a	Adult Dosage	Comments
Bismuth subsalicylate (Pepto-Bismol)	2 tablets, or 60 mL liquid suspension, orally, four times a day	Less effective than antibiotic prophylaxis; contraindicated in people allergic to aspirin, taking other salicylate-containing drugs, or who are pregnant. Not recommended for children.
Fluoroquinolone ^b Ciprofloxacin 500 mg Norfloxacin 400 mg Ofloxacin 200 mg Levofloxacin 500 mg	1 tablet once daily	Contraindicated in pregnancy and in people allergic to quinolones; beware of drug interaction with theophylline and caffeine.
Rifaximin 200 mg	1-2 tablets daily	Only 0.4% absorbed. Should be safe in pregnancy (not studied). Where Campylobacter is prevalent, 2 tablets daily is preferred owing to high MICs of the organism (not studied)

MIC, Minimum inhibitory concentration.

a Both trimethoprim-sulfamethoxazole and doxycycline showed benefit in prophylaxis in old studies; rising resistance among enteropathogens around the world has now rendered these drugs passé.

b All fluoroquinolones should work equally well.

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