Rainfall and Temperature Modify Effects of On-Site Sanitation Intervention on E. coli Contamination in Bangladeshi Households

Weather events associated with climate change can influence the environmental spread and survival of fecal pathogens, potentially impacting the efficacy of water, sanitation, and hygiene (WASH) interventions. We used longitudinal data from a randomized controlled trial in Bangladesh to assess whether rainfall and temperature modified the effect of an on-site sanitation intervention on fecal contamination. Over 3.5 years, we enumerated E. coli in household samples along eight fecal-oral pathways (n=23,238 samples) and obtained daily weather data. The intervention included the provision of double-pit latrines, child potties, and scoops for removing child and animal feces, along with behavior change promotion. The intervention was associated with larger reductions in E. coli in/on mother hands, child hands, ponds, and flies (0.10-log to 0.91-log) following higher rainfall and in/on food, mother hands, child hands, soil, and ponds (0.11-log to 0.40-log) following higher temperatures, compared to drier and colder periods. The intervention slightly reduced E. coli in stored drinking water and had no consistent effect on E. coli in tubewell water, regardless of weather. Our findings suggest that sanitation interventions can help mitigate the effects of increased rainfall and temperature on environmental fecal contamination. Previous analyses of these data without stratification by daily weather only found small (approximately 0.10-log) reductions in E. coli in/on stored drinking water and child hands. Future WASH trials should incorporate weather data to identify periods of differential intervention effectiveness to understand how weather variability influences the outcomes of public health interventions and develop strategies to enhance resilience against climate change impacts in vulnerable communities. Research in ContextO_ST_ABSEvidence before this studyC_ST_ABSHigher temperatures and increased rainfall linked to climate change have been associated with increased infectious disease transmission. Effective water, sanitation, and hygiene (WASH) interventions, such as access to improved sanitation facilities, are pivotal in reducing these risks. However, the efficacy of WASH interventions in interrupting fecal-oral transmission can be influenced by weather fluctuations, which can compromise service delivery and/or exacerbate environmental dissemination of fecal waste. We conducted a literature review on the impact of weather events and climate change on the environmental spread of fecal pathogens and their influence on WASH interventions. We used Google Scholar to identify articles published from 2000 to 2024 using the following search terms: ("climate change" OR weather OR weather events OR temperature OR heatwave OR rainfall OR precipitation) AND (sanitation OR "WASH intervention" OR "sanitation intervention" OR "intervention efficacy") AND (pathogen OR enteropathogen OR "Escherichia coli" OR "E. coli" OR "fecal indicator" OR "fecal contamination" OR "fecal pathogens). Studies have documented the influence of weather conditions, particularly rainfall and temperature, on the effectiveness of WASH interventions in reducing fecal contamination and diarrhea. A recent meta-analysis found that lack of access to improved latrines and piped drinking water modified the association between rainfall/temperature and diarrhea incidence in children under the age of five but this analysis only focused on health outcomes and did not include measures of environmental contamination. In Bangladesh, WASH interventions, including water treatment and handwashing, were more effective in reducing E. coli contamination in stored drinking water and food during dry seasons compared to wet seasons, however, in a different longitudinal analysis focused on a sanitation intervention, seasonality did not significantly modify the relationship between the intervention and fecal contamination. However, these studies used seasonal definitions (wet vs. dry) which can miss transient weather fluctuations within a season. One study in Kenya used daily rainfall and temperature data to show that increases in drinking water contamination associated with increased rainfall were mitigated if households treated their water. No study has evaluated the influence of daily weather parameters on the effect of WASH improvements on a comprehensive set of fecal-oral pathways. Added value of this studyThis study utilizes longitudinal data from a randomized controlled trial that implemented water treatment, handwashing and sanitation interventions in Bangladesh (WASH Benefits), with over 23,000 E. coli measurements collected over 3.5 years. The measurements were taken along eight fecal-oral transmission pathways, including mother and child hands, stored food, stored drinking water, groundwater from tubewells, ponds, courtyard soil, and captured flies. Previous analyses of these data with no stratification by daily weather found only small reductions in environmental fecal contamination associated with the WASH interventions. In the present analysis, we re-analyzed these data using daily weather measurements to investigate whether rainfall and temperature modified the efficacy of the improved on-site sanitation intervention in reducing E. coli contamination in the domestic environment. Unlike previous analyses that did not consider daily weather variations, stratifying by daily weather conditions revealed differential intervention impacts on E. coli contamination, with larger reductions observed following periods of higher rainfall and temperature across multiple fecal-oral pathways (mother hands, child hands, food, soil, ponds, and flies). Implications of all the available evidenceUnderstanding how interventions perform under varying weather conditions is crucial, particularly in low- and middle-income countries susceptible to extreme weather events. Integrating fine-grained weather data into sanitation intervention assessments can inform climate adaptation strategies. Our findings, combined with evidence from previous studies, indicate that on-site sanitation improvements, water treatment and broader WASH approaches can help protect against environmental fecal contamination associated with increased rainfall and temperatures. These insights are pivotal for designing resilient WASH interventions capable of mitigating climate-related health risks in vulnerable populations, supporting the Sustainable Development Goals in low- and middle-income countries. The WASH Benefits sanitation interventions implemented in rural Bangladesh demonstrated enhanced efficacy during periods of higher rainfall and temperature. These effects were not discernible in previous analyses that did not stratify by daily weather, where average reductions in E. coli counts were minimal, underscoring the importance of capturing weather variability in assessing intervention impacts. This approach also contrasts with earlier studies using calendar-based definitions of seasons, which may not fully capture the nuanced effects of climate variables on intervention efficacy. Collectively, these findings underscore the importance of incorporating fine-grained weather data in WASH trials to enhance the understanding of intervention efficacy under variable environmental conditions.