Food and water precautions
A broad range of diseases may be acquired by consuming contaminated food or water. When traveling in developing countries, it is essential to exercise discretion in the choice of meals and beverages.
Do not drink tap water unless it has been boiled, filtered, or chemically disinfected. Vigorous boiling for one minute is the most effective means of water purification. At altitudes greater than 6500 feet (2 km), boil for three minutes.
Chemical disinfection with iodine is also effective. Add 2% tincture of iodine to one quart or liter of water (5 drops to clear water, 10 drops to cloudy water) and let stand for 30 minutes. If the water is cold, longer times may be required. (To kill cryptosporidia, which are an important cause of illness in those infected with HIV, let stand for 15 hours.) Alternatively, tetraglycine hydroperiodide tablets (iodine pills)i, such as Globaline, Potable-Aqua, and Coghlan's, may be purchased at most pharmacies. Instructions are enclosed and should be carefully followed. The taste of iodinated water may be improved by adding vitamin C (ascorbic acid). Iodinated water should not be consumed for more than a few weeks. Pregnant women, those with a history of thyroid disease, and those allergic to iodine should not drink iodinated water.
A number of water filters are available. Those with smaller pores (reverse osmosis filters) provide the broadest protection, but they are relatively large and are readily plugged by debris. Those with somewhat larger pores (microstrainer filters) are ineffective against viruses, although they remove other organisms. Objective data comparing different filters is limited. In all instances, manufacturers' instructions must be carefully followed for the filters to operate effectively.
Do not drink unbottled beverages or drinks with ice. Do not eat fruits or vegetables unless they have been peeled or cooked. Avoid cooked foods that are no longer piping hot. Cooked foods that have been left at room temperature are particularly hazardous. Avoid unpasteurized milk and any products that might have been made from unpasteurized milk, such as ice cream. Do not eat raw or undercooked meat or fish. Avoid food and beverages obtained from street vendors.
Avoid tropical reef fish, even when cooked. Ciguatera fish poisoning is caused by a toxin present in a large number of tropical reef fish. Symptoms typically occur 1-6 hours after eating contaminated fish and may include nausea, vomiting, abdominal pain, diarrhea, numbness, tingling and leg weakness. Since the toxin is tasteless and odorless and is not inactivated by cooking or freezing, the only means of prevention is not to eat tropical reef fish. Barracuda in particular should always be avoided. Other fish that may contain ciguatoxin include red snapper, grouper, kingfish, amberjack, sea bass, moray eel, and sturgeon. Another type of fish poisoning is scombroid, which may occur after inadequate refrigeration or preservation of a number of different fish, including mackerel, bluefin, yellowfin tuna, bonito, mahimahi, herring amberjack, and bluefish. Symptoms may include flushing, headache, nausea, vomiting, diarrhea, and hives.
From the World Health Organization (WHO)
Food-borne and water-borne health risks (in chapter "Environmental Health Risks")
Guide on Safe Food for Travelers
Safe food for travellers
From the Centers for Disease Control (CDC)
Treatment of Water to Make it Safe for Drinking
Risks from Food and Water
Food Poisoning from Marine Toxins
From the National Travel Health Network and Centre (U.K.)
Toxic fish poisoning
From Health Canada
Gastrointestinal Illness While Traveling
Ciguatera Fish Poisoning