Contaminated food and drink are common sources for the introduction of infection into the body. Among the more common infections that travelers may acquire from contam-inated food and drink are Escherichia coli infections, shigellosis or bacillary dysentery, giardiasis, cryptosporidiosis, and hepatitis A. Other less common infectious disease risks for travelers include typhoid fever and other salmonelloses, cholera, infections caused by rotaviruses and Norwalk-like viruses, and a variety of protozoan and helminth parasites (other than those that cause giardiasis and cryptosporidiosis). Many of the infectious diseases transmitted in food and water can also be acquired directly through the fecal-oral route.

Water
Water that has been adequately chlorinated, using minimum recommended water-works standards as practiced in the United States, will afford significant protection against viral and bacterial waterborne diseases. However, chlorine treatment alone, as used in the routine disinfection of water, may not kill some enteric viruses and the parasitic organisms that cause giardiasis, amebiasis and cryptosporidiosis. In areas where chlo-rinated tap water is not available, or where hygiene and sanitation are poor, travelers should be advised that only the following may be safe to drink:

1. Beverages, such as tea and coffee, made with boiled water
2. Canned or bottled carbonated beverages, including carbonated bottled water and soft drinks
3. Beer and wine

Where water may be contaminated, ice should also be considered contaminated and should not be used in beverages. If ice has been in contact with containers used for drinking, the containers should be thoroughly cleaned, preferably with soap and hot water, after the ice has been discarded.

It is safer to drink directly from a can or bottle of a beverage than from a questionable container. However, water on the outside of beverage cans or bottles might be contami-nated. Therefore, wet cans or bottles should be dried before being opened, and surfaces which are contacted directly by the mouth in drinking should first be wiped clean. Where water may be contaminated, travelers should avoid brushing their teeth with tap water.

Treatment of water
Boiling is by far the most reliable method to make water of uncertain purity safe for drinking. Water should be brought to a vigorous rolling boil for one minute and allowed to cool to room temperature—do not add ice. At altitudes above 6,562 feet (2 km), for an extra margin of safety, boil for three minutes or use chemical disinfection. Adding a pinch of salt to each quart, or pouring the water several times from one container to another will improve the taste.

Chemical disinfection with iodine is an alternative method of water treatment when it is not feasible to boil water. Two well-tested methods for disinfection with iodine are the use of tincture of iodine (Table 25), and the use of tetraglycine hydroperiodide tablets (Globaline, Potable-Agua, Coghlan's*, etc.). The tablets are available from pharmacies and sporting goods stores. The manufacturer's instructions should be followed. If water is cloudy, the number of tablets should be doubled; if water is extremely cold, an attempt should be made to warm the water, and the recommended contact time should be increased to achieve reliable disinfection. Cloudy water should be strained through a clean cloth into a container to remove any sediment or floating matter, and then the water should be boiled or treated with iodine. Chlorine, in various forms, has also been used for chemical disinfection. However, its germicidal activity varies greatly with pH, temperature, and organic content of the water to be purified, and is less reliable than iodine.

There are a variety of portable filters currently on the market which according to the manufacturers' data will provide safe drinking water. Although the iodide-impregnated resins and the microstrainer type filters will kill and/or remove many micoorganisms, very few published reports in the scientific literature deal both with the methods used and the results of the tests employed to evaluate the efficacy of these filters against pathogens. Until there is sufficient independent verification of the efficacy of these filters, CDC makes no recommendation regarding their use in the general population.

As a last resort, if no source of safe drinking water is available or can be obtained, tap water that is uncomfortably hot to touch may be safer than cold tap water; however, proper disinfection or boiling is still advised.

Food
To avoid illness, food should be selected with care. All raw food is subject to contamina-tion. Particularly in areas where hygiene and sanitation are inadequate, the traveler should be advised to avoid salads, uncooked vegetables, unpasteurized milk and milk products such as cheese, and to eat only food that has been cooked and is still hot, or fruit that has been peeled by the traveler. Undercooked and raw meat, fish, and shellfish may carry various intestinal pathogens. Cooked food that has been allowed to stand for several hours at ambient temperature may provide a fertile medium for bacterial growth and should be thoroughly reheated before serving. Consumption of food and beverages obtained from street food vendors has been associated with increased risk of illness. The easiest way to guarantee a safe food source for an infant less than 6 months of age is to have the child breast-feed. If the infant has already been weaned from the breast, formula prepared from commercial powder and boiled water is the safest and most practical food.

Some species of fish and shellfish can contain poisonous biotoxins, even when well cooked. The most common type of fish poisoning in travelers is ciguatera fish poisoning. Barracuda is the most toxic fish and should always be avoided. Red snapper, grouper, amberjack, sea bass, and a wide range of tropical reef fish contain the toxin at unpredictable times. The potential for ciguatera poisoning exists in all subtropical and tropical insular areas of the West Indies, Pacific and Indian Oceans where the implicated fish species are consumed.

Cholera cases have occurred among persons who ate crab brought back from Latin America by travelers. Travelers should not bring perishable seafoods with them when they return.

* Use of tradenames is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.