Adherence to solar disinfection water treatment reduces diarrheal incidence among children in Malawi : a secondary analysis of a cluster quasi-experimental study

Background: Diarrhoea is a leading cause of morbidity and mortality among children under five in low-income regions. This study assessed the effectiveness of household solar disinfection (SODIS) in reducing diarrhoeal incidence among children in Chikwawa District, Malawi. Methods: We conducted a secondary analysis of a cluster quasi-experimental trial (March 2019–March 2020) involving 985 children from 793 households: control (369 children, 271 households), 20 L transparent polypropylene SODIS bucket (336 children, 258 households), and SODIS bucket with cloth filter (380 children, 264 households). Variables included water source, child age, sex, rotavirus vaccination, SODIS adherence. Analyses employed descriptive statistics, Chi-square, Kruskal–Wallis tests, and Poisson regression with robust standard errors in Stata 17. Results: Overall, diarrhoeal incidence was two cases per child-year. Households using SODIS buckets had an 88% reduction in incidence (adjusted incidence rate ratio (IRR): 0.12; 95% CI: 0.04–0.23), while those using SODIS with a cloth filter saw a 70% reduction (adjusted IRR: 0.30; 95% CI: 0.18–0.50). High SODIS adherence was linked to 90% reduction (adjusted IRR: 0.13; 95% CI: 0.02–0.81); medium adherence showed no significant effect. Conclusion: These findings support SODIS as an effective point-of-use water treatment, with adherence critical to health impact.