Influence of climate and environment on the efficacy of water, sanitation, and handwashing interventions on diarrheal disease in rural Bangladesh: a re-analysis of a randomized control trial

BackgroundDiarrheal disease is a leading cause of childhood morbidity and mortality globally. Household water, sanitation, and handwashing (WASH) interventions can reduce exposure to diarrhea-causing pathogens, but climatic factors may impact their effectiveness. Information about effect heterogeneity under different weather conditions is critical to intervention targeting. MethodsWe analyzed data from a trial in rural Bangladesh that compared child diarrhea prevalence between clusters that were randomized to different WASH interventions between 2012-2016 (NCT01590095). We matched temperature and precipitation measurements to households by geographic coordinates and date. We estimated prevalence ratios (PR) using generative additive models and targeted maximum likelihood estimation to assess the effectiveness of each WASH intervention under different environmental conditions. FindingsGenerally, WASH interventions most effectively prevented diarrhea during monsoon season, particularly following weeks with heavy rain or high temperatures. Compared to the control arm, WASH interventions reduced diarrhea by 51% (95% CI 33%-64%) following periods with heavy rainfall vs. 13% (95% CI -26%-40%) following periods without heavy rainfall. Similarly, WASH interventions reduced diarrhea by 40% (95% CI 16%-57%) following above-median temperatures vs. 17% (95% CI -38%-50%) following below-median temperatures. The influence of precipitation and temperature varied by intervention type; for precipitation, the largest differences in effectiveness were for the sanitation and combined WASH interventions. InterpretationWASH intervention effectiveness was strongly influenced by precipitation and temperature, and nearly all protective effects were observed during the rainy season. Future implementation of these interventions should consider local environmental conditions to maximize effectiveness. FundingBill & Melinda Gates Foundation; National Institute of Allergy and Infectious Diseases; National Heart, Lung, And Blood Institute; National Institute of General Medical Sciences; Stanford University School of Medicine; Chan Zuckerberg Biohub Research in Context PanelO_ST_ABSEvidence before this studyC_ST_ABSWe searched Google Scholar using the search terms "sanitation" OR "hygiene" OR "WASH" OR "water quality"; AND "heterogen*" OR "effect modif*"; AND "temperature" OR "precipitation" OR "rain*" OR "climate" OR "environmental"; AND "diarrhea" OR "enteric infection"; AND "risk" AND/OR "factors". In general, the effect modification of WASH interventions on diarrhea by weather is not well studied. One study in Ecuador investigated different relationships between rainfall, diarrhea, and unimproved sanitation and water sources. They found that unimproved sanitation was most strongly associated with elevated diarrhea after low rainfall, whereas unimproved water sources were most strongly associated with elevated diarrhea after heavy rainfall. In a similar setting in Ecuador, a separate study found that drinking water treatments reduced increases in diarrhea after heavy rainfall that followed dry periods, while sanitation and hygiene had no impact on the relationship between heavy rainfall and diarrhea. One study in Rwanda also found that high levels of runoff were protective against diarrhea only in households with unimproved toilets. In Bangladesh, one study found that access to tubewells was most effective at reducing childhood diarrhea in non-flood controlled areas. High heat can accelerate the inactivation of enteric pathogens by water chlorination, but no studies have examined how temperature influences the effectiveness of sanitation or hygiene interventions. No prior studies have estimated differences in WASH effectiveness under varying weather conditions within a randomized trial. Added value of this studyTo our knowledge, this is the first study to assess differences in household-level WASH intervention effectiveness by weather conditions in a randomized trial. We spatiotemporally matched individual-level data from a trial in rural Bangladesh to remote sensing data on temperature and precipitation and estimated differences in the effectiveness of WASH interventions to prevent childhood diarrhea under varying levels of these environmental factors. Implications of all the available evidenceWe found that WASH interventions were substantially more effective following periods with higher precipitation or higher temperatures. We observed the largest effect modification by precipitation for a sanitation intervention. This may be because compared to water and handwashing interventions, the sanitation intervention blocked more pathways through which enteric pathogens reach water, soil, and flies following heavy rainfall. In regions like Bangladesh, extreme weather is expected to become more common under climate change but WASH interventions might mitigate increases in childhood diarrhea due to climate change.