Installing insecticidal nets around eaves, windows and wall openings in houses that have not been remodelled is a potential malaria control measure. It can prevent mosquitoes from entering houses, have lethal and sublethal effects on malaria vectors and potentially reduce malaria transmission. Therefore, we conducted an epidemiological study in Tanzanian households to evaluate the effectiveness of indoor insecticide screening (ITS) against malaria and vectors.
A household consisted of one or more houses, each managed by a head of household, with all household members sharing common kitchen facilities. Households were eligible for the study if they had open eaves, unbarred windows, and intact walls. All household members aged 6 months or older were included in the study, excluding pregnant women who were undergoing routine screening during antenatal care according to national guidelines.
From June to July 2021, to reach all households in each village, data collectors, guided by village chiefs, went door-to-door interviewing households with open eaves, unprotected windows, and standing walls. One adult household member completed a baseline questionnaire. This questionnaire included information on the location and characteristics of the house, as well as the socio-demographic status of household members. To ensure consistency, the informed consent form (ICF) and questionnaire were assigned a unique identifier (UID), which was printed, laminated, and attached to the front door of each participating household. The baseline data were used to generate a randomization list, which guided the installation of the ITS in the intervention group.
Malaria prevalence data were analyzed using a per-protocol approach, excluding from the analysis individuals who had traveled in the past two weeks or taken antimalarial medication in the two weeks prior to the survey.
To determine the impact of ITS across different housing types, ITS use, and age groups, we conducted stratified analyses. Malaria incidence was compared between households with and without ITS within a defined stratification: mud walls, brick walls, traditional roofs, tin roofs, those using ITS the day before the survey, those not using ITS the day before the survey, young children, school-aged children, and adults. In each stratified analysis, age group, sex, and the relevant household stratification variable (wall type, roof type, ITS use, or age group) were included as fixed effects. Household was included as a random effect to account for clustering. Importantly, the stratification variables themselves were not included as covariates in their own stratified analyses.
For indoor mosquito populations, unadjusted negative binomial regression models were only applied to the daily number of mosquitoes captured per trap per night due to the small number of mosquitoes captured throughout the assessment.
Households were screened for malaria infection in the short and long term, with results showing households that were visited, refused to be visited, accepted to be visited, lost to visit due to relocation and long-distance travel, participant refusal to be visited, use of antimalarial drugs, and travel history. Households were surveyed for indoor mosquitoes using CDC light traps, with results showing households that were visited, refused a visit, accepted a visit, were lost to visit due to moving, or were absent for the entire survey period. ITS was installed in control households.
In Chalinze District, no significant differences were found in malaria infection rates or indoor mosquito populations between households with an insecticide-treated screening system (ITS) and those without. This may be due to the study design, the insecticidal and residual properties of the intervention, and the high number of participants who dropped out of the study. Although the differences were not significant, lower levels of parasite infestation were found at the household level during the long rainy season, which was more pronounced among school-aged children. Indoor Anopheles mosquito populations also decreased, suggesting the need for further research. Therefore, a cluster-randomized study design combined with active community engagement and outreach is recommended to ensure retention of participants throughout the study.
Post time: Aug-19-2025