The incidence density of
infection and disease caused by Plasmodium falciparum in children aged six to 24 months living in the holoendemic Sahel of northern Ghana was measured during the wet and dry seasons of 1996 and 1997. At the beginning of each season, a cohort composed of 259 and 277 randomly selected children received supervised curative
therapy with
quinine and
Fansidar and
primaquine for those with normal
glucose-6-phosphate dehydrogenase activity. The 20 weeks of post-
therapy follow-up consisted of three home visits weekly and examination of Giemsa-stained blood films once every two weeks. Blood films were also taken from children brought to clinic with illness. The incidence density of
parasitemia after radical cure was 4.7
infections/person-year during the dry season and 7.1 during the wet season (relative risk = 1.51, 95% confidence interval [CI] = 1.25-1.81; P = 0.00001). Although the mean
parasitemia count at time of
reinfection in the dry season (3,310/microl) roughly equaled that in the wet season (3,056/microl; P = 0.737), the risk ratio for
parasitemia > 20,000/microl during the wet season was 1.71 (95% CI = 1.2-2.4; P = 0.0025). The risk ratio for
parasitemia > 20,000/microl with
fever during the wet season was 2.45 (95% CI = 1.5-4.1; P = 0.0002). The risk ratio for
anemia (
hemoglobin < 8 g/dl) at first post-radical cure
parasitemia showed no difference between seasons (1.0; 95% CI = 0.73-1.4; P = 0.9915). We did not see seasonal differences in
anemia known to exist in this region, probably because the longitudinal cohort design using first
parasitemia as an end point prevented the subjects from developing the repeated or
chronic infections required for
anemia induction. These findings bear upon the design of
malaria drug and
vaccine trials in holoendemic areas.