A household randomised-control trial of insecticide-treated screening for malarial control in unimproved houses in Tanzania

Background Insecticide-treated screening of gaps, including open eaves, windows, and holes in walls of unimproved houses, prevents mosquitoes' indoor entry, and induces lethal and sub-lethal effects to malaria vectors, and may potentially impact malaria transmission. Therefore, a household epidemiological trial was conducted to assess the efficacy of the Insecticide-treated screening on malaria infection and vector in Tanzania. Methods A total of 421 households from Chalinze district, Tanzania were randomly allocated to two arms. One group of houses was fitted with insecticide-treated screening (incorporated with 2g AI/kg deltamethrin and 8g/kg piperonyl butoxide synergist) on their open eaves, windows, and wall holes, while the second group did not receive screening. Consented members (aged 6 months and above) in all households were tested for malaria infection using quantitative polymerase chain reaction (qPCR) after the long rain season (June/July 2022, primary outcome) and the short rain season (January/February 2022, secondary outcome). Additional secondary outcomes include the indoor mosquito density after the long rainy season, adverse effects after one month of ITS installation, and quality of ITS after one year of field use. At the end of the trial, the control group received screening. The trial was registered at ClinicalTrials.gov (NCT05125133). Results Malaria infection prevalence among residents in the ITS arm was 19.9% (50/251) and 28.3% (65/230) in the control arm after the long rainy season, however, this was not significant [adjusted OR 0.67 (95% CI: 0.35–1.28), p = 0.227]. Similarly, during the short rainy season, no protection was also seen for ITS (p = 0.452). The intervention was safe, with no serious adverse effects recorded. There was no significant difference in the average number of female Anopheles mosquitoes caught per day of the survey in the houses with screening compared to those without was 1.7 vs 2.4 [Crude Relative Risk: 0.71 (95% CI: 0.16–3.09)]. ITS showed reduced chemical retention and efficacy post-field use. Conclusion The trial was inconclusive, possibly because households' refusal to be surveyed resulted in low power. A large cluster randomised trial of the intervention, preferably with a longer-lasting insecticidal effect, is needed. Trial registration: The trial was registered at ClinicalTrials.gov (NCT05125133) on October 2021.