Malaria Risk and the Role of Routine Outdoor Nocturnal Activities and Livelihoods among Adults in Dar es Salaam, Tanzania

Abstract

Humans become infected with malaria upon receiving infectious bites from blood-feeding female anopheline mosquitoes. The human-mosquito contact is directly attributable to individual lifestyles and although predominantly domestic, it may also occur outside houses. Indoor malaria transmission has been largely subdued across large parts of Africa through wide scale coverage of insecticide treated nets (ITNs) and indoor residual spraying (IRS). Nonetheless, increasing evidence shows outdoor biting mosquitoes often dominate residual transmission systems and undermine efforts to achieve elimination of malaria transmission. Effective interventions which target outdoor malaria transmission are available but remain unproven in rigorous epidemiological terms. This study assessed malaria risk among the residents of Dar es Salaam and established the impact upon malaria prevalence of routine oytd06r nightly activities and ~omrnon livelihoods ~...., among adults. A baseline cross-sectional daytime survey and evening follow-ups were conducted and data collected through one-~n-one interviews based on structured questionnaires. Malaria risk was estimated as a function of the proportion of exposure that ~ occurs indoors (ni) and in bed (ns). Predictive variables were analysed by binary logistic regression against blood test outcomes obtained through rapid diagnosis and microscopy. Individuals spent more time indoors sleeping at night and higher risk of malaria occurred during these hours. There was estimated lower but significant outdoor exposure with both ni and ns strongly predictive of prevalence (p<O.OOI). Spending I to 2 hours outdoors during evenings doubled the risk of malaria infection (p<O.OOl, O!3:.~2.162 95~ CI: 1.685-2.773). I Resting outdoors during evenings was a routine activity trnong most adults and increased malaria risk. Most households used bednets as the key malaria protective measure. However, . livelihoods were not associated with prevalence of malaria. Improved surveillance and control of outdoor exposure IS requisite for malaria elimination in Dar es Salaam.