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Imported Malaria among Travelers -- United States

From 1973 through 1983, 2,575 cases of malaria were reported among U.S. citizens who were infected while traveling abroad. This was 33% of all imported cases reported during this period--the majority occurring among foreign nationals. Of the cases among U.S. citizens, 849 (33%) had been infected with Plasmodium falciparum. During this period, the number of P. falciparum infections among U.S. travelers rose almost sevenfold from 21 cases in 1973 to 139 in 1983. The increase has been especially marked among U.S. travelers who visited east Africa: in 1973-1974 only nine cases occurred among such travelers, compared with 88 cases in 1982-1983 (a nearly 10-fold increase). Infections with P. falciparum malaria in nonimmune individuals can be extremely serious and potentially fatal: 31 deaths from malaria occurred among the 849 patients with P. falciparum infections, for a case-fatality ratio of 4%.

In 1982-1983, more than half of all P. falciparum cases in the United States were imported from five countries: Kenya (61 cases), Haiti (26), Tanzania (19), Nigeria (15), and Ghana (10); 167 (68%) of the 247 P. falciparum infections among U.S. travelers were acquired in Africa. Attack rates for certain years can be estimated for Kenya, Ghana, and Haiti based on the number of U.S. travelers to those countries as provided by the World Tourism Organization in Madrid. The estimated number of malaria infections in U.S. travelers to Kenya increased from 21.2 per 100,000 travelers in 1977 to 83.3/100,000 in 1982; for Ghana, the estimated number of malaria infections was 104.4/100,000 U.S. visitors in 1977-1978; for Haiti, the number was 19.2/100,000 in 1982.

Importation of malaria is not only a problem in the United States. For instance, the number of imported cases of malaria into Great Britain increased from 100 in 1970 to 1,471 in 1982. Between 1970 and 1980, 88% of the P. falciparum infections reported in Great Britain originated in Africa (1).

Travelers who acquire malaria generally do not take appropriate chemoprophylaxis. For example, only 8% of the U.S. travelers who acquired P. falciparum malaria in west Africa or Haiti between 1981 and 1983 had histories of having taken chloroquine chemoprophylaxis during their travels. Reduced efficacy of chemoprophylaxis may also factor in the increased importation of malaria from certain areas, especially east Africa: the percentage of patients who reportedly had used chloroquine as chemoprophylaxis while traveling in east Africa increased from 22% in 1977 to 76% in 1983. This trend has been reviewed recently by CDC and has necessitated changes in recommendations for chemoprophylaxis for U.S. travelers to defined areas of east Africa (2). Reported by Malaria Br, Div of Parasitic Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The risk of malaria to travelers can be reduced through adequate use of effective chemoprophylactic drugs. This requires that travelers to malarious countries be adequately informed about malaria risks and malaria chemoprophylaxis and that they be motivated to adhere to recommendations. Information about health risks and chemoprophylaxis is provided through official publications from CDC (3,4) and the World Health Organization (5). Little is known, however, about traveler awareness of the risk in malarious areas, about the advice, if any, they receive about chemoprophylaxis and from which sources, and whether some categories of travelers (e.g., missionaries, Peace Corps volunteers) may be better informed than other groups (e.g., tourists, business travelers). Because of the large number of U.S. international travelers and the great diversity in the U.S. travel industry, efficient dissemination of information to help protect the health of the traveling public is difficult.

In increasing areas of the world, chloroquine can no longer be considered an effective drug to prevent P. falciparum malaria. Chloroquine-resistant P. falciparum is known to exist in the following countries: Bolivia, Burma, Burundi, Colombia, Comoros, Ecuador, French Guyana, Kampuchea, Kenya, Laos, Madagascar, Malaysia, Papua New Guinea, Rwanda, Solomon Islands, Surinam, Tanzania, Thailand, Uganda, Vanuatu, Venezuela, Vietnam, and in parts of Bangladesh, Brazil, China, India, Malawi, Mozambique, Panama, Peru, the Philippines, Sudan, Zaire, and Zambia. Weekly use of the combination drug, pyrimethamine-sulfadoxine (FansidarR), in addition to weekly use of chloroquine, is recommended by CDC for travelers to these areas (5).

An update of CDC's recommendations (2) regarding chemoprophylaxis will be published soon as an MMWR Supplement, "Prevention of Malaria in Travelers, 1984."

References

  1. Bruce-Chwatt LJ. Imported malaria: an uninvited guest. Br Med Bull 1982;38:179-92.

  2. CDC. Update: chloroquine-resistant Plasmodium falciparum--Africa. MMWR 1983;32:437.

  3. CDC. Prevention of malaria in travelers, 1982. MMWR Supplement 1982;31:1S-28S.

  4. CDC. Health information for international travel, 1983. Atlanta, Georgia: Centers for Disease Control, 1983; HHS publication no. (CDC) 83-8280.

  5. World Health Organization. Vaccination certificate requirements for international travel and health advice to travellers. Geneva, Switzerland: World Health Organization, 1983.



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