A household randomized-control trial of insecticide-treated screening for malaria control in unimproved houses in Tanzania

Background: Installing insecticidal netting on open eaves, windows, and holes in walls of unimproved houses is a potential malaria control tool. It prevents mosquito house-entry, induces lethal and sub-lethal effects on malaria vectors, and may reduce malaria transmission. Therefore, a household epidemiological trial was conducted to assess the efficacy of insecticide-treated screening (ITS) on malaria infection and indoor vectors in Tanzania. Methods: In Chalinze district, Tanzania, 421 households were randomized into two arms. In June-July 2021, one group of households’ houses was fitted with ITS (incorporated with deltamethrin and piperonyl butoxide) on eaves, windows, and wall holes, while the second group did not receive screening. After installation, consenting household members (aged ≥ 6 months) were tested for malaria infection using quantitative polymerase chain reaction after the long rainy season (June/July 2022, primary outcome) and the short rainy season (January/February 2022, secondary outcome). Secondary outcomes included indoor total mosquito per trap/night (June–July 2022), adverse effects after one month of ITS installation (August 2021), and chemical bioavailability and retention of ITS samples after one year of field use (June/July 2022). At the end of the trial, the control group received ITS. Results: Malaria prevalence among residents in the ITS arm was 19.9% (50/251) and 28.3% (65/230) in the control arm after the long rains, however, this difference was not significant [adjusted odds ratio (OR) 0.67 (95% CI 0.35–1.28), p = 0.227]. Similarly, no protection was seen for ITS after the short rains, [OR 1.27 (95% CI 0.68–2.38), p = 0.452]. However, school-age children in the ITS arm had lower malaria after the long rains [OR 0.11 (95% CI 0.02–0.73), p = 0.022]. No serious adverse effects were reported. The mean number of female Anopheles mosquitoes caught per trap/night was not significantly different between arms [1.7 vs 2.4, crude relative risk: 0.71 (95% CI 0.16–3.09), p = 0.650]. ITS showed reduced chemical bioavailability and retention post-field use. The trial reported high household refusals (17–30%) in both arms in both surveys. Conclusion: The trial was inconclusive because households' refusal resulted in low power. A large cluster randomized trial of the intervention, preferably with screens treated with longer-lasting insecticides installed in houses, is needed. Trial registry: The trial was registered at ClinicalTrials.gov (NCT05125133) on October 2021