Rainfall and temperature influence effectiveness of on-site sanitation intervention against E. coli contamination in Bangladeshi households

Weather can influence the environmental spread and survival of fecal pathogens, potentially affecting the effectiveness of water, sanitation, and hygiene (WASH) interventions. We assessed whether rainfall and temperature modified effects of an on-site sanitation intervention on fecal contamination among households in the WASH Benefits trial in rural Bangladesh. The intervention included double-pit latrines, potties, feces removal tools and behavior change promotion. We longitudinally visited households from intervention and control groups to enumerate E. coli. Samples (n = 23,238) included drinking water from tubewells and storage containers, prepared food, caregiver and child hand rinses, pond water, courtyard soil, and flies. We geospatially matched E. coli measurements to daily weather data and estimated intervention effects with and without stratification by weather. The intervention resulted in greater reduction in contamination following higher rainfall for four pathways (mother/child hands, ponds, flies), and following higher temperatures for five pathways (food, mother/child hands, soil, ponds). Compared to controls, E. coli levels were reduced by approximately 1-log for flies and 0.25-log in ponds after higher rainfall, 0.2-log on child hands, 0.3–0.4 log in soil and ponds after higher temperatures (interaction p-values<0.20), and 0.1-log in stored drinking water under most conditions. Intervention effects were minimal when not stratified by weather, with <0.1-log reductions for stored drinking water and child hands, and no effects on other pathways. Sanitation interventions may deliver greater protection against environmental contamination during wetter, warmer conditions, and assessments that average over time may conceal differential intervention effects. WASH trials should incorporate spatiotemporal weather data into impact evaluations.