Malaria field studies in a high-incidence coastal area of El Salvador, C.A.

A three-year investigation was made of the incidence patterns and characteristics of malaria in a small high-incidence coastal area of El Salvador with a resident population of about 6,000 persons and a migrant population of 3,000 to 4,000 others. It found a significant increase in the incidence of Plasmodium falciparum cases during the three-year period, combined with relative stability in the annual number of Plasmodium vivax cases. A close correlation was observed between the seasonal occurence of P. falciparum cases in 1973 and vector densities, and between vector densities and aerial application of agricultural insecticides. Cases of P. vivax appeared about twice as common in the 5 to 14 year age group as in older or younger groups, and cases of P. falciparum seemed only about one-third as frequent in the 0 to 4 year group as in older groups. The attack rate in 1973 was somewhat higher in males than in females. There appeared to be a decrease in parasite densities with age, as well as a direct correlation between parasite densities and the degree of disability (symptoms and "in bed" time) reported by patients.