Impact of Multiplicity of Plasmodium falciparum Infection on Clinical Disease in Malawi

Multiplicity of infection (MOI), the number of unique Plasmodium falciparum parasite genotypes found in one infected individual, may contribute to the development of clinical malaria disease. However, the independent contribution of MOI and parasite density to clinical disease has not been well characterized. We conducted a two-year longitudinal cohort study of adults and children in a high-transmission setting in Malawi to test the hypothesis that increased MOI was independently associated with clinical disease, after accounting for parasite density. Of 1,062 episodes of infection, 477 (44.9%) were associated with symptoms. After controlling for repeated measures within an individual, key demographic factors, and parasite density, there was no association between MOI and clinical disease (OR = 1.02, 95% CI: 0.70-1.51). Although the limited ability to discern MOI in low-density asymptomatic infections may have impacted our results, we conclude that MOI is not an independent risk factor for clinical disease.