Molecular Evaluation of the Natural History of Asymptomatic Parasitemia in Ugandan Children

We assessed the prevalence and natural history of malarial parasitemia by use of microscopy and polymerase chain reaction (PCR) in 314 asymptomatic children in Kampala, Uganda. The prevalence of asymptomatic parasitemia was 17% by microscopy and 47% by PCR. Children with parasitemia identified by microscopy had a 5-fold higher rate of subsequent symptomatic malaria, compared with children without detectable parasitemia. Children with parasitemia identified by PCR alone had a similar rate of subsequent symptomatic malaria, compared with children without detectable parasitemia. Among microscopy-positive children who later developed symptomatic malaria, 47% had strains identical to those identified at enrollment, and the proportion of symptomatic episodes due to persistent strains remained high for 3 months. Among the PCR-positive/microscopy-negative children, only 17% had identical genotyping patterns at the onset of symptomatic malaria, with most of these episodes occurring during the first month. Asymptomatic parasitemia detected by microscopy, but not by PCR, strongly predicted subsequent clinical malaria, often due to persistent infection.