Traveler's Diarrhea - Prevention

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. 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.
• 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. 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.
• Avoid green salads, because it is unlikely that the lettuce will have been washed with bottled water.

If handled properly, well-cooked and packaged foods are usually safe. 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.

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. 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. 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.

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. 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.

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). Also, antibiotics can cause a disease called pseudomembranous colitis which results in severe, unrelenting diarrhea.

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.

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. Several vaccine candidates targeting enterotoxigenic E. coli (ETEC) and Shigella are in various stages of development.

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. 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 and direct interaction with the host gut epithelium, preventing the attachment and invasion of gastrointestinal pathogens. 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.