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.