International Notes Update: Cholera Outbreak -- Peru, Ecuador, and Colombia

The following report is reprinted from the Weekly Epidemiological Record of the World Health Organization (WHO). The editorial note was prepared by CDC.

SMALL RISK OF CHOLERA TRANSMISSION BY FOOD IMPORTS WHO has no documented evidence of a cholera outbreak occurring as a result of the importation of food across international borders.

• Dried, acidic and pickled foods, fruit juices: cholera

organisms are sensitive to drying and to acidity (pH less than 4.5); therefore, these foods and juices are unlikely to cause infection.

• Coffee, cereals: same as for dried foods above.

• Frozen foods: freezing below -20 centigrade will reduce, but may not completely eliminate, cholera organisms from food.

• Canned foods: canned foods produced according to the relevant Codex standard* are free of cholera organisms even if the raw product was contaminated.

• Irradiated foods: irradiated foods produced according to the relevant Codex standard** and which have received a dose of at least 1kGy are free of cholera organisms even if the raw product was contaminated.

• Fresh sea food: sea food from shallow coastal waters (such as prawns and shellfish) may be contaminated. It should be properly cooked as shown below. Deep sea fish are unlikely to have been infected in their habitat, but could become contaminated during subsequent handling.

• Fresh vegetables and fruit: these may be surface contaminated and may remain so up to a maximum of 10 days.

• Animal feeds: since there is no known reservoir of cholera in poultry or livestock, animal feeds, and in particular dried fish meal, do not pose a risk of transmission.

Cholera transmission through food can be eliminated by thorough cooking (core temperature 70 centigrade), and by prevention of contamination of cooked foods by contact with raw foods or infected food handlers. Refrigeration prevents multiplication of the cholera organism but may prolong its survival. Fruit from which the peel can be removed should also be safe.

If national authorities are concerned about the importation of any product, they are urged to consult with the World Health Organization, Food Safety unit, 1211 Geneva 27, Switzerland, or with the Pan American Health Organization, Program Coordinator, HST, 525 Twenty-Third Street, NW, Washington, DC 20037-2897, United States of America (Fax (202) 223-5971).

Countries are reminded that cholera vaccine is not recommended as a measure for prevention or control and they should not require it from persons entering or leaving infected countries. On no account should the travel of people across frontiers be restricted because of cholera. Reprinted from: World Health Organization. Weekly Epidemiological Record 1991;66:55-6. Reported by: Enteric Diseases Br, Div of Bacterial and Mycotic Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: In late January 1991, cholera appeared in South America for the first time this century (1). It was first identified in Peru and has now spread to Ecuador and Colombia (Figure 1). Because all three countries export food, there has been concern that food from these countries might infect consumers. WHO published the above report to respond to this concern; CDC concurs with the statements in the WHO report.

The duration of survival of Vibrio cholerae O1 in food is affected by several factors, including pH, humidity, temperature, and inoculum size. Many vibrios are needed to infect a person who has normal gastric acidity. Most imported foods, even if contaminated with V. cholerae O1 at the point of origin, pose minimal risk to the consumer. Bivalve molluscan shellfish eaten raw are the food most likely to carry V. cholerae O1 and infect consumers. In 1988, raw oysters shipped from the U.S. coast on the Gulf of Mexico caused single cases of cholera in six states (2). The U.S. Food and Drug Administration's (FDA) National Shellfish Sanitation Program does not sanction any imports of bivalve molluscan shellfish from Peru, Ecuador, and Colombia.

Cholera may spread to additional countries in South America, and a small number of U.S. residents may acquire the disease during travel or by eating imported food. Treatment of cholera is simple and highly effective, with case-fatality rates of less than 1% when proper oral and/or intravenous rehydration therapy is given. Sanitation in the United States is adequate to make the risk of continued transmission extremely small; none of the cholera cases imported into the United States since 1961 have resulted in secondary transmission (3). Sporadic cases of cholera that have occurred in the United States since 1973 have been associated with consumption of seafood from the Gulf coast; only one outbreak of cholera (on a floating oil rig) has been traced to fecal contamination (4).

In response to the situation in Peru, in mid-February, FDA substantially increased its surveillance of food imports to safeguard consumers in the United States by increasing sampling and testing of crustaceans, finfish, and produce from Peru for V. cholerae O1.

The risk of cholera to tourists is extremely low (3), and cholera vaccine is not recommended for persons traveling to affected countries. Careful selection of safe foods and beverages is paramount (5).

References

1. CDC. Cholera--Peru, 1991. MMWR 1991;40:108-10.

2. CDC. Toxigenic Vibrio cholerae O1 infection acquired in Colorado. MMWR 1989;38:19-20.

3. Snyder JD, Blake PA. Is cholera a problem for US travelers? JAMA 1982;247:2268-9.

4. Johnston JM, Martin DL, Perdue J, et al. Cholera on a Gulf Coast oil rig. N Engl J Med 1983;309:523-6.

5. CDC. Health information for international travel, 1990. Atlanta: US Department of Health and Human Services, Public Health Service, 1990:141-3; DHHS publication no. (CDC)90-8280.

• Recommended International Code of Practice for Low-Acid and Acidified Low-Acid Canned Food, Codex Alimentarius Vol. G, FAO/WHO 1983.

** Codex General Standard for Irradiated Foods, and Recommended International Code of Practice for the Operation of Radiation Facilities used for the Treatment of Foods, Codex Alimentarius Vol. XV, FAO/WHO 1984.

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