Assessment of the incidence and prevalence of clinical malaria in semi-immune children exposed to intense and perennial transmission.

In order to determine the incidence and prevalence of clinical malaria in children exposed since birth to intense and perennial transmission, two successive longitudinal surveys, a weekly survey over four months and a daily survey over 10 days, were carried out in 1983-1984 among 182 children aged 5-13 years in Linzolo, Republic of the Congo, a village where malaria is holoendemic. By age group, prevalence of clinical malaria was found to be between 3.2% and 2.4% at ages 5-6 years, between 2.5% and 1.8% at ages 7-8 years, between 1.6% and 1.1% at ages 9-10 years, and between 0.5% and 0.3% at ages 11-13 years. For these four age groups, respectively, the annual incidence of clinical malaria was estimated during the first survey as 3.0, 2.1, 1.8, and 1.2 attacks, and during the second survey as 5.2, 2.7, 2.0, and 0.8 attacks. No difference was observed in the incidence of malarial attacks between children who use bed-nets and those who do not use them. Also investigated were the customs of the inhabitants of the village in the presence of febrile syndromes in the children, and the importance of antimalarial drug consumption in these cases. It was observed that almost all of these syndromes were rapidly treated with antimalarials, and that in half of the cases these drugs were administered by the parents themselves.