Longitudinal Assessment of Asymptomatic Malaria Infections in a Suburban Community in Lagos, Nigeria

Malaria remains a public health concern. Asymptomatic individuals are significant reservoirs for onward transmission of malaria. Subclinical infections are directly detrimental to the health of individuals and populations. For effective malaria control, it is crucial to understand the burden of asymptomatic malaria (AM). This study assessed the seasonal prevalence of AM in a suburban community in Lagos, Nigeria. A total of 1,860 asymptomatic individuals were screened for Plasmodium falciparum using a rapid diagnostic test (RDT), microscopy and polymerase chain reaction (PCR). The overall detection rates using microscopy, RDT, and PCR were 2.7% (50/1860, 95%CI: 1.9-3.4), 8.8% (163/1860, 95%CI: 7.5-10.0), and 11.7% (218/1860, 95%CI: 10.3-13.2), respectively. Using PCR outcomes as the ground truth, RDT has a higher sensitivity when compared with microscopy (34.4% versus 22.0%). Although the two methods have high specificity, microscopy has a higher positive predictive value (96.0%) compared to RDT, at 46%. AM infection was more frequent during the wet season (14.9%), with a peak in June at 36.0% (54/150). In contrast, during the dry season, the rate was 7.2%. The frequency of AM was high among the school-age group (5-14 years), at 14.1%. AM carriage was more common in males, at 12.9%, compared to females, at 10.7%. This study presents evidence of a high frequency of AM infection during the wet season and among male individuals residing in Lagos. Curbing the onward transmission of the disease requires increased surveillance for AM nationwide to estimate its frequency, with a focus on younger individuals, especially during the wet season.