The epidemiology of febrile malaria episodes in an area of unstable and seasonal transmission

This study investigated the epidemiology of uncomplicated falciparum malari a in an area of unstable and seasonal transmission in eastern Sudan. About 90% of malaria morbidity in this region occurs in the months of September t o November, and very few malaria cases occur during the intensely arid Suda nese dry season and during years of drought. The malaria situation in the s tudy sire, the village of Daraweesh, was analysed during 3 consecutive mala ria seasons in 1993-95 during which the 457 inhabitants suffered a total of 436 episodes of falciparum malaria. Using an Andersen-Gill proportional ha zard model for recurrent events stratified by family, we have calculated th e relative hazard for clinical malaria episodes by age, sex, haemoglobin ge notype, blood type and infection in the previous season. The malaria risk w as significantly lower in individuals aged 20-88 years than in the 5-19 yea rs age-group. The relative protection due to adulthood varied between seaso ns (relative risk, RR, 0.34 to 0.67). Serological data were not consistent with the hypothesis that the age difference in incidence was due to differe nces in exposure. During the 1993 season the malaria incidence in males was lower than in females (RR = 0.75), during the 1994 season the incidences w ere comparable, whereas males had an increased risk of malaria in 1995 (RR = 1.87). The relative risk in individuals carrying the haemoglobin AS genot ype compared to homozygous AA individuals was 0.57.