A large-scale longitudinal cohort project was initiated in western Kenya in June 1992. Between June
1992 and July 1994, 1,848 children less than 15 years of age were monitored prospectively for a mean of 236 days.
During this period, 12,035 blood smears were examined for malaria and only 34% were found to be negative. Parasite
prevalence (all species) decreased with age (from a high of 83% among children 1–4 years old to 60% among
children 10–14 years old). Even more dramatic decreases were noted in the prevalence of high density falciparum
infection (from 37% among children 12–23 months old to , 1% among 10–14-year-old children) and in clinical
malaria (20% to 0.3% in the same age groups). Children , 1 year of age accounted for 55% of all cases of anemia
detected. Anemia was consistently associated with high density infection in children , 10 years of age (20% to 210%
increased risk relative to aparasitemic children). These results demonstrate the relationship between high-density
malaria infection and two clinical manifestations of malarial illness.