Associations between weather extremes and faecal contamination along pathogen transmission pathways in rural Bangladeshi households: a prospective observational study.

Background: Weather extremes are predicted to influence pathogen exposure but their effects on specific faecal-oral transmission pathways are not well investigated. We evaluated associations between extreme rain and temperature during different antecedent periods (0-14 days) and Escherichia coli along eight faecal-oral pathways in rural Bangladeshi households.

Methods: We used data from the WASH Benefits Bangladesh cluster-randomised controlled trial (NCT01590095). E coli was enumerated in hand rinses from children younger than 5 years and their mothers, food, stored drinking water, tubewells, captured flies, ponds, and courtyard soil using IDEXX Quanti-Tray/2000 in nine rounds over 3·5 years and spatiotemporally matched to daily weather data. We used generalised linear models with robust standard errors to estimate E coli count ratios (ECRs) associated with extreme rain and temperature, defined as greater than the 90th percentile of daily values during the study period.

Findings: A total of 26 659 samples were collected during the study period. Controlling for temperature, extreme rain on the sampling day was associated with increased E coli in food (ECR=3·13 [95% CI 1·63-5·99], p=0·0010), stored drinking water (ECR=1·98 [1·36-2·88], p=0·0004), and ponds (ECR=3·46 [2·34-5·11], p<0·0001), and reduced E coli in soil (ECR=0·36 [0·24-0·53], p<0·0001). Extreme rain the day before sampling was associated with reduced E coli in tubewells (ECR=0·10 [0·02-0·62], p=0·014). Associations were similar for rainfall 1-7 days before sampling and slightly attenuated for rainfall 14 days before sampling. Controlling for rainfall, extreme temperature on the sampling day was associated with increased E coli in stored drinking water (ECR=1·49 [1·05-2·12], p=0·025) and food (ECR=3·01 [1·51-6·01], p=0·0020). Associations with temperature were similar for all antecedent periods and particularly pronounced for food. Neither rainfall nor temperature were consistently associated with E coli on hands and flies.

Interpretation: In rural Bangladesh, measures to control enteric infections following weather extremes should focus on water treatment and safe storage to reduce contamination of drinking water and food stored at home and on reducing exposure to surface waters.

Funding: Bill & Melinda Gates Foundation, National Institutes of Health, World Bank.