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Epidemiologic studies were done in two localities, one in Panama and one in El Salvador, where outbreaks of Plasmodium falciparum malaria occurred. The indirect fluorescent antibody (IFA) method was helpful in defining the intensity of the outbreaks, the species of parasite involved, and, through parallel surveys of adjacent localities, the localized character of the outbreaks. In Escobal, Panama 71 (34%) of 211 persons examined were IFA-positive for P. falciparum, although only 1 positive blood film was seen in this survey. In Jocomontique, El Salvador, 15 (28%) of 53 persons examined were IFA-positive for P. falciparum; 6 persons were parasite-positive. In the Panama study a number of children with positive IFA titers at the time of the epidemic had reverted to negative 6 months later. This lability of titers in children, probably resulting from very early treatment of their first infection and, thus, a very brief exposure to the parasite antigen, suggests the need for caution in interpreting such negative serologic findings. Serologic studies provide valuable information in malaria epidemics, but must be interpreted in association with other known epidemiologic factors in the area concerned.
Present address: Bureau of Tropical Diseases, Center for Disease Control, 1600 Clifton Road, Atlanta, Georgia 30333.