Health Information for International Travel

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 contaminated 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 rotavirus and Norwalk-like viruses, and a variety of protozoan and helminthic 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 waterworks 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 chlorinated 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 contaminated. 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 1 minute and allowed to cool to room temperature—do not add ice. At altitudes higher than 6,562 feet (2 km), for an extra margin of safety, boil for 3 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. However, this method cannot be relied on to kill Cryptosporidium unless the water is allowed to sit for 15 hours before drinking it. Two well-tested methods for disinfection with iodine are the use of tincture of iodine (see table below) and the use of tetraglycine hydroperiodide tablets (e.g., Globaline^®, Potable-Aqua^®, and Coghlan’s ^®). These 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 the pH, temperature, and organic content of the water to be purified, and it is less reliable than iodine. Chemically treated water is intended for short-term use only. If iodine-disinfected water is the only water available, it should be used for only a few weeks.

Treatment of water with tincture of iodine

Portable filters currently on the market will provide various degrees of protection against microbes. Reverse-osmosis type filters provide protection against viruses, bacteria, and protozoa, but they are expensive, are larger than most filters used by backpackers, and the small pores on this type of filter are rapidly plugged by muddy or cloudy water. In addition, the membranes in some filters can be damaged by chlorine in water. Microstrainer filters with pore sizes in the 0.1- to 0.3-micrometer range can remove bacteria and protozoa from drinking water, but they do not remove viruses. To kill viruses, users of microstrainer filters are advised to disinfect the water after filtration with iodine or chlorine as described above. Filters with iodine-impregnated resins are most effective against bacteria; the iodine will kill some viruses, but the contact time with the iodine in the filter is too short to kill Giardia in cold water and will not kill Cryptosporidium. Proper selection, operation, care, and maintenance of water filters is essential to producing safe water. The manufacturers’ instructions should be followed. NSF International, an independent testing company, tests and certifies water filters for their ability to remove protozoa (Giardia and Cryptosporidium), but not for their ability to remove bacteria or viruses. Few published reports in the scientific literature have evaluated the efficacy of specific brands or models of filters against bacteria and viruses in water. Until such information becomes available, CDC cannot identify which specific brands or models of filters are most likely to remove bacteria and viruses. For more information about how to select a proper water filter, read the CDC brochure entitled “You can prevent cryptosporidiosis”. A list of filters that have passed NSF tests for parasite removal is available at the NSF International web site. Printed versions can be obtained by calling 1-800-673-8010 or by writing to NSF at 3475 Plymouth Road, P.O. Box 130140, Ann Arbor, MI  48113-0140.

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, filtering, or boiling is still advised.

Food

To avoid illness, food should be selected with care. All raw food is subject to contamination. Particularly in areas where hygiene and sanitation are inadequate, the traveler should be advised to avoid salads, uncooked vegetables, and 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 younger than 6 months is to breast-feed the child . 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, the Pacific Ocean, and the Indian Ocean where the implicated fish species are eaten.

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