Asymptomatic Plasmodium falciparum malaria prevalence among adolescents and adults in Malawi, 2015-2016

Abstract

Malaria remains a significant cause of morbidity and mortality in Malawi, with an estimated 18-19% prevalence of Plasmodium falciparum in children 2-10 years in 2015-2016. While children report the highest rates of clinical disease, adults are thought to be an important reservoir to sustained transmission due to persistent asymptomatic infection. The 2015-2016 Malawi Demographic and Health Survey was a nationally representative household survey which collected dried blood spots from 15,125 asymptomatic individuals ages 15-54 between October 2015 and February 2016. We performed quantitative polymerase chain reaction on 7,393 samples, detecting an overall P. falciparum prevalence of 31.1% (SE = 1.1). Most infections (55.6%) had parasitemias ≤ 10 parasites/µL. While 66.2% of individuals lived in a household that owned a bed net, only 36.6% reported sleeping under a long-lasting insecticide-treated net (LLIN) the previous night. Protective factors included urbanicity, greater wealth, higher education, and lower environmental temperatures. Living in a household with a bed net (prevalence difference 0.02, 95% CI - 0.02 to 0.05) and sleeping under an LLIN (0.01; - 0.02 to 0.04) were not protective against infection. Our findings demonstrate a higher parasite prevalence in adults than published estimates among children. Understanding the prevalence and distribution of asymptomatic infection is essential for targeted interventions.

Figure 1

Distribution of PCR P. falciparum positive parasitemia values (n = 2215). Values < 10 parasites/µL are rounded up to 10 parasites/µL. The density plot’s solid line represents a normal distribution using the observed counts.

Figure 2

Spatial distribution of 2015–2016 MDHS clusters. (a) P. falciparum prevalence by cluster and cluster size, (b) weighted P. falciparum prevalence by district, (c) smoothed PCR P. falciparum prevalence estimates using simple kriging, (d) smoothed P. falciparum standard error estimates using simple kriging. Clusters with fewer than five observations were removed prior to kriging to reduce the influence of extreme values due to small sample sizes. Smoothed surfaces are meant to demonstrate regional differences and should not be used for interpretation into areas where data do not exist. All maps were run using R 3.5.1 (R Foundation for Statistical Computing, Vienna, Austria) and the sf (v0.9–2; Pebesma, 2020) package.