safe water. Avoid green salads, because the lettuce and other uncooked ingredients are unlikely to have been washed with safe water. Avoid eating raw fruits and vegetables unless cleaned and peeled personally. If handled properly, thoroughly cooked fresh and packaged foods are usually safe. 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 and beverages purchased from street vendors and other establishments where unhygienic conditions may be present. Water Although safe bottled water is now widely available in most remote destinations, travelers can treat their own water if necessary, or as an extra precaution. Techniques include boiling, filtering, chemical treatment, and ultraviolet light; boiling is by far the most effective of these methods. Boiling rapidly kills all active bacteria, viruses, and protozoa. Prolonged boiling is usually unnecessary; most microorganisms are killed within seconds at water temperature above 55–70 °C (130–160 °F). The second-most effective method is to combine filtration and chemical disinfection. Filters eliminate most bacteria and protozoa, but not viruses. Chemical treatment with halogens—chlorine bleach, tincture of iodine, or commercial tablets—have low-to-moderate effectiveness against protozoa such as Giardia, but work well against bacteria and viruses. UV light is effective against both viruses and cellular organisms, but only works in clear water, and it is ineffective unless manufacturer's instructions are carefully followed for maximum water depth/distance from UV source, and for dose/exposure time. Other claimed advantages include short treatment time, elimination of the need for boiling, no taste alteration, and decreased long-term cost compared with bottled water. The effectiveness of UV devices is reduced when water is muddy or turbid; as UV is a type of light, any suspended particles create shadows that hide microorganisms from UV exposure. Medications Bismuth subsalicylate four times daily reduces rates of travelers' diarrhea. Though many travelers find a four-times-per-day regimen inconvenient, lower doses have not been shown to be effective. Potential side effects include black tongue, black stools, nausea, constipation, and ringing in the ears. Bismuth subsalicylate should not be taken by those with aspirin allergy, kidney disease, or gout, nor concurrently with certain antibiotics such as the quinolones, and should not be taken continuously for more than three weeks. Some countries do not recommend it due to the risk of rare but serious side effects. A hyperimmune bovine colostrum to be taken by mouth is