Malaria in the Limbé River valley of northern Haiti: a hospital-based retrospective study, 1975-1997.

In the Limbé River valley of northern Haiti a retrospective study at the Bon Samaritain Hospital (BSH) determined the total number of cases and the cyclical nature of malaria from 1975 through 1997, examined the relationship between rainfall and malaria from 1975 through 1985, and compared the incidence of malaria at that hospital with general trends for Haiti for 1975 through 1996 as reported by the World Health Organization (WHO). During 1975-1997, 27,078 positive cases of malaria were diagnosed at BSH; 50% of these cases occurred during 16 weeks out of the year, during a summer peak in June and July and a winter peak in December and January. For 1975-1985, there was no significant correlation between the incidence of malaria and annual rainfall. The strongest correlation was observed between weekly rainfall and weekly incidence of malaria when the data was staggered to allow a lag of 9-11 weeks between rainfall and new malaria cases. The lag period is explained by the time required for the creation of breeding sites after rain, the life cycles of the Anopheles albimanus mosquito and the Plasmodium falciparum parasite, and the incubation period for falciparum malaria. The incidence of malaria in the Limbé River valley loosely followed the trends in all of Haiti and also supported WHO reports indicating that malaria in Haiti has been in a general decline since the mid-1980s. By showing the seasonal trends for malaria in the Limbé valley and the relationship between rainfall and malaria over an extended time period, this study provides a means to measure the effectiveness of malaria control efforts in the region.