Asymptomatic parasitaemia as a risk factor for symptomatic malaria in a cohort of Ugandan children

OBJECTIVES To assess the prevalence of asymptomatic parasitaemia, determine its association with symptomatic malaria, and identify independent predictors of asymptomatic parasitaemia in a cohort of children from Kampala, Uganda. METHODS A total of 316 children aged 6 months to 5 years were recruited from the community. The prevalence of asymptomatic parasitaemia was assessed at enrolment and approximately every 30 days during follow-up. Participants received all of their health care in our clinic, including a standardized approach to the diagnosis and treatment of symptomatic malaria. RESULTS A total of 283 (90%) subjects completed the full 1-year follow-up and were included in this study, yielding 2557 routine smears. The prevalence of asymptomatic parasitaemia was 17% at enrolment, but 5-8% for the remainder of the study. The risk of developing symptomatic malaria within 30 days was significantly higher in those with a positive routine than in those with a negative one (50%vs. 9%, P < 0.001). Higher parasite densities were associated with increased odds of developing symptomatic malaria within 30 days (P = 0.003). Only 11% of episodes of asymptomatic parasitaemia, involving 6% of subjects, arose and cleared without therapy. In multivariate analysis the only significant risk factor for asymptomatic parasitaemia was whether a child had any episode of symptomatic malaria during the course of the study (OR = 3.0, P = 0.02). CONCLUSION In our cohort of children from an urban meso-endemic environment, asymptomatic parasitaemia was uncommon and frequently followed by symptomatic malaria. This suggests that presumptive treatment of asymptomatic parasitaemia in such settings would be an efficient means of preventing symptomatic malaria.