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

Background Climate change may influence the effectiveness of environmental interventions. We investigated if climate and environment modified the effect of low-cost, point-of-use water, sanitation, and handwashing (WASH) interventions on diarrhea and predicted intervention effectiveness under climate change scenarios. Methods We analyzed data from a cluster-randomized trial in rural Bangladesh that measured diarrhea prevalence in children 0-2 years from 2012-2016. We matched remote sensing data on temperature, precipitation, humidity, and surface water to households by location and measurement date. We estimated prevalence ratios (PR) for WASH interventions vs. control stratified by environmental factors using generative additive models and targeted maximum likelihood estimation. We estimated intervention effects under predicted precipitation in the study region in 2050 for climate change scenarios from different Shared Socioeconomic Pathways (SSPs). Findings WASH interventions more effectively prevented diarrhea under higher levels of total precipitation in the previous week and when there was heavy rain in the previous week (heavy rainfall PR = 0.38, 95% CI 0.23-0.62 vs. no heavy rainfall PR = 0.77, 0.60-0.98). We did not detect substantial effect modification by other environmental variables. WASH intervention effectiveness increased under most climate change scenarios; in a fossil-fueled development scenario (SSP5), the PR was 0.46 (0.44-0.48) compared to 0.67 (0.65-0.68) in the study. Interpretation WASH interventions had the strongest effect on diarrhea under higher precipitation, and effectiveness may increase under climate change without sustainable development. WASH interventions may improve population resilience to climate-related health risks. Funding Bill & Melinda Gates Foundation, National Institute of Allergy and Infectious Diseases, National Heart, Lung, And Blood Institute Evidence before this study We searched Google Scholar using the search terms “sanitation” OR “hygiene” OR “WASH” OR “water quality”; and “heterogen*” or “effect modif*”; and “climate” OR “environmental”; and “diarrhea” OR “enteric infection”; and “risk” AND/OR “factors”. In general, the effect modification of sanitation and hygiene on diarrhea or enteropathogen infection by climate and environment is not well studied. One study in Ecuador investigated different relationships between rainfall, diarrhea, and unimproved sanitation and water sources. They found that poor sanitation was most strongly associated with elevated diarrhea after precipitation minimums, whereas poor water sources were most strongly associated with elevated diarrhea after precipitation maximums. 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. No prior studies have projected changes in WASH effectiveness under different climate change scenarios. Added value of this study To our knowledge, this is the first study to assess differences in WASH intervention effectiveness for multiple environmental variables and the first to predict future intervention effectiveness under different climate change scenarios. We spatiotemporally matched individual-level data from a trial in rural Bangladesh to remote sensing data on temperature, precipitation, humidity, and surface water presence. We compared the effectiveness of WASH interventions to prevent diarrhea under different levels of potential environmental effect modifiers. We then used climate models with high spatiotemporal resolution to predict changes in intervention effectiveness under different climate change scenarios. Implications of all the available evidence We found that WASH interventions were more effective under increasing precipitation and following heavy rain (over 80th percentile) events. Prior studies have found that diarrhea tends to increase with rainfall. Several studies have documented that precipitation-associated increases in diarrhea occurred primarily after heavy rain that followed dry periods, but we found that WASH intervention effectiveness in preventing diarrhea was higher even at moderate precipitation levels that were not necessarily preceded by a dry period. Under climate change scenarios with higher precipitation, we projected that WASH interventions may become more effective. In settings similar to rural Bangladesh, our findings suggest that regions that are expected to experience greater rainfall should be prioritized for intervention installation, promotion, and maintenance and that these activities might be most impactful during the rainy season. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial NCC01590095 ### Funding Statement This study was supported by the Gates Foundation (grant number OPPGD759 to the University of California, Berkeley) and the Task Force for Global Health (grant number NTDSC 088G to Innovations for Poverty Action, and grant number NTDSC 089G to the University of California, Berkeley). Research reported in this publication was supported in part by the National Institute of Allergy And Infectious Diseases of the National Institutes of Health under Award Numbers K01AI141616 (PI: Benjamin-Chung) and R01AI166671 (PI: Arnold), the National Heart, Lung, And Blood Institute of the National Institutes of Health under award number T32HL151323 (Nguyen), and a Stanford University School of Medicine Dean's Postdoctoral Fellowship (Grembi). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Jade Benjamin-Chung is a Chan Zuckerberg Biohub Investigator. We also acknowledge the Stanford Research Computing Center for computational resources at the Sherlock high-performance cluster. The funders of the study had no role in study design, data analysis, interpretation, writing of the manuscript, or the decision to submit the manuscript for publication. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The original trial protocol was approved by the Ethical Review Committee at The International Centre for Diarrhoeal Disease Research, Bangladesh (PR-11063), the Committee for the Protection of Human Subjects at the University of California, Berkeley (2011-09-3652), and the institutional review board at Stanford University (25863).  I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Individual participant data and metadata for this study will be made available at the time of publication and posted here: https://osf.io/yt67k/ The pre-analysis plan and ancillary results are also available at the same URL. To protect participant privacy, household geocoordinates will not be included in the public dataset.