Insecticide-treated net effectiveness at preventing Plasmodium falciparum infection varies by age and season

Andrea G Buchwald,Kondwani Nkanaunena,Jenny A Walldorf,Lauren M Cohee,John D Sorkin,Terrie E Taylor,Jenna E Coalson,Nelson Chimbiya,Don P Mathanga,Andrew Ngwira,Andy Bauleni,Miriam K Laufer

doi:10.1186/s12936-017-1686-2

Abstract

BackgroundAfter increasing coverage of malaria interventions, malaria prevalence remains high in Malawi. Previous studies focus on the impact of malaria interventions among children under 5 years old. However, in Malawi, the prevalence of infection is highest in school-aged children (SAC), ages 5 to 15 years. This study examined the interaction between age group and insecticide-treated net (ITN) use for preventing individual and community-level infection in Malawi.MethodsSix cross-sectional surveys were conducted in the rainy and dry seasons in southern Malawi from 2012 to 2014. Data were collected on household ITN usage and demographics. Blood samples for detection of Plasmodium falciparum infection were obtained from all household members present and over 6 months of age. Generalized linear mixed models were used to account for clustering at the household and community level.ResultsThere were 17,538 observations from six surveys. The association between ITN use and infection varied by season in SAC, but not in other age groups. The adjusted odds ratio (OR) for infection comparing ITN users to non-users among SAC in the rainy season and dry season was 0.78 (95% CI 0.56, 1.10) and 0.51 (0.35, 0.74), respectively. The effect of ITN use did not differ between children under five and adults. Among all non-SACs the OR for infection was 0.78 (0.64, 0.95) in those who used ITNs compared to those that did not. Community net use did not protect against infection.ConclusionsProtection against infection with ITN use varies by age group and season. Individual estimates of protection are moderate and a community-level effect was not detected. Additional interventions to decrease malaria prevalence are needed in Malawi.

Highlights

After increasing coverage of malaria interventions, malaria prevalence remains high in Malawi
School-aged children (SAC), aged 5–15 years, make up ~30% of the population, and recent data from Malawi show that they have the highest infection prevalence, at 4.8 times the odds of infection compared to other ages [14]
Given the contribution of school-aged children (SAC) to overall Plasmodium prevalence and the age-based differences in behaviour and exposure there is a need for research into age-related variations in the impact of insecticide-treated net (ITN) use on infection prevalence

Summary

Introduction

After increasing coverage of malaria interventions, malaria prevalence remains high in Malawi. Previous studies have found that even after universal net distribution, SAC were significantly less likely to use ITNs compared to other age groups [19]. When previous studies have included wider age ranges, with children both under and over five, the results for impact of community ITN ownership and household ITN ownership on population-wide infection prevalence have been non-significant [20,21,22]. This may be related to behavioural differences in net use between age groups or persistence of prevalent infections among SAC. Given the contribution of SAC to overall Plasmodium prevalence and the age-based differences in behaviour and exposure there is a need for research into age-related variations in the impact of ITN use on infection prevalence

Methods

Results

Conclusion