Abstract
Indoor residual spraying (IRS) and long-lasting insecticide-treated bednets (LLINs) are common tools for reducing malaria transmission. We studied a cohort in Uganda with universal access to LLINs after 5 years of sustained IRS to explore LLIN adherence when malaria transmission has been greatly reduced. Eighty households and 526 individuals in Nagongera, Uganda were followed from October 2017 -October 2019. Every two weeks, mosquitoes were collected from sleeping rooms and LLIN adherence the prior night assessed. Episodes of malaria were diagnosed using passive surveillance. Risk factors for LLIN non-adherence were evaluated using multi-level mixed logistic regression. An age-matched case-control design was used to measure the association between LLIN non-adherence and malaria. Across all time periods, and particularly in the last 6 months, non-adherence was higher among both children <5 years (OR 3.31, 95% CI: 2.30-4.75; p<0.001) and school-aged children 5-17 years (OR 6.88, 95% CI: 5.01-9.45; p<0.001) compared to adults. In the first 18 months, collection of fewer mosquitoes was associated with non-adherence (OR 3.25, 95% CI: 2.92-3.63; p<0.001), and, in the last 6 months, residents of poorer households were less adherent (OR 5.1, 95% CI: 1.17-22.2; p = 0.03). Any reported non-adherence over the prior two months was associated with a 15-fold increase in the odds of having malaria (OR 15.0, 95% CI: 1.95 to 114.9; p = 0.009). Knowledge about LLIN use was high, and the most frequently reported barriers to use included heat and low perceived risk of malaria. Children, particularly school-aged, participants exposed to fewer mosquitoes, and those from poorer households, were less likely to use LLINs. Non-adherence to LLINs was associated with an increased risk of malaria. Strategies, such as behavior change communications, should be prioritized to ensure consistent LLIN use even when malaria transmission has been greatly reduced.
Highlights
Long lasting insecticide-treated bednets (LLINs) are a mainstay of malaria prevention [1]
We studied a cohort in Uganda with universal access to LLINs after 5 years of sustained Indoor residual spraying (IRS) to explore LLIN adherence when malaria transmission has been greatly reduced
The number of LLINs was not measured after enrollment, but was assumed to be adequate to cover all sleeping areas due to on demand distribution to cohort participants
Summary
Long lasting insecticide-treated bednets (LLINs) are a mainstay of malaria prevention [1]. Despite increasingly robust programs for the universal distribution of LLINs, the impressive declines in malaria transmission achieved from 2000 to 2015 have recently stalled and may be reversing, especially in high burden African countries [2]. This stall in progress in malaria reduction has highlighted the importance of other tools for vector control such as indoor residual spraying of insecticides (IRS). A subgroup analysis from the comprehensive review, demonstrated that in populations with high LLIN adherence (reported use > 50%), adding IRS was associated with a substantial reduction in parasite prevalence, with a risk ratio of 0.47 (95% confidence interval [CI]: 0.33 to 0.67) compared to populations without IRS. The benefits of combining IRS with LLINs may depend on the levels of LLIN adherence
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