Impact on childhood mortality of interventions to improve drinking water, sanitation, and hygiene (WASH) to households: Systematic review and meta-analysis.

Background: In low- and middle-income countries (L&MICs), the biggest contributing factors to the global burden of disease in childhood are deaths due to respiratory illness and diarrhoea, both of which are closely related to use of water, sanitation, and hygiene (WASH) services by households. However, current estimates of the health impacts of WASH interventions use self-reported morbidity, which may fail to capture longer-term or more severe impacts. Reported mortality is thought to be less prone to bias than other reported measures. This study aimed to answer the question: What are the impacts of WASH interventions on reported childhood mortality in L&MICs? Methods and findings: We conducted a systematic review and meta-analysis, using a published protocol. Systematic searches of 11 academic databases and trial registries, plus organisational repositories, were undertaken to locate studies of WASH interventions, which were published in peer review journals or other sources (e.g., organisational reports and working papers). Intervention studies of WASH improvements implemented under endemic disease circumstances in L&MICs were eligible, which reported findings at any time until March 2020. We used the participant flow data supplied in response to journal editors' calls for greater transparency. Data were collected by two authors working independently. We included evidence from 24 randomized and 11 nonrandomized studies of WASH interventions from all global regions, incorporating 2,600 deaths. Effects of 48 WASH treatment arms were included in analysis. We critically appraised and synthesised evidence using meta-analysis to improve statistical power. We found WASH interventions are associated with a significant reduction of 17% in the odds of all-cause mortality in childhood (OR = 0.83, 95% CI = 0.74, 0.92, evidence from 38 interventions), and a significant reduction in diarrhoea mortality of 45% (OR = 0.55, 95% CI = 0.35, 0.84; 10 interventions). Further analysis by WASH technology indicated interventions providing improved water in quantity to households were most consistently associated with reductions in all-cause mortality. Community-wide sanitation was most consistently associated with reductions in diarrhoea mortality. Around one-half of the included studies were assessed as being at "moderate risk of bias" in attributing mortality in childhood to the WASH intervention, and no studies were found to be at "low risk of bias." The review should be updated to incorporate additional published and unpublished participant flow data. Conclusions: The findings are congruent with theories of infectious disease transmission. Washing with water presents a barrier to respiratory illness and diarrhoea, which are the two biggest contributors to all-cause mortality in childhood in L&MICs. Community-wide sanitation halts the spread of diarrhoea. We observed that evidence synthesis can provide new findings, going beyond the underlying data from trials to generate crucial insights for policy. Transparent reporting in trials creates opportunities for research synthesis to answer questions about mortality, which individual studies of interventions cannot be reliably designed to address. Hugh Sharma Waddington and colleagues investigate the impacts of water, sanitation and hygiene interventions on all-cause and diarrhoea-related mortality in low- and middle-income countries. Author summary: Why was this study done?: The biggest contributor to the global burden of infectious disease in childhood in developing countries is mortality due to respiratory and diarrhoeal infections, both of which are closely linked to deficient water, sanitation, and hygiene (WASH) availability and use by households. Multiple systematic reviews and meta-analyses of WASH-related morbidity have been conducted, but there is a shortage of rigorous, systematic evidence on the effectiveness of WASH interventions in reducing mortality. What did the researchers do and find?: We conducted a systematic review and meta-analysis of the impacts of WASH interventions on all-cause and diarrhoea-related mortality in L&MICs, incorporating evidence from 35 studies comprising 48 distinct WASH intervention arms. We found significant effects on all-cause mortality among children aged under 5 of interventions to improve the quantity of water available (34% reduction), hygiene promotion when water supplies were accessible to households (29% reduction), and community-wide sanitation (21% reduction). We also found significant effects of WASH interventions on diarrhoea mortality among under 5s (45% reduction), which were significantly larger when provided to communities that were at the lowest rungs of the sanitation ladder, compared to those that already had improved WASH. What do these findings mean?: Interventions to prevent water-related mortality in childhood in endemic disease circumstances provide adequate water supplies to households, enabling domestic hygiene and safe excreta disposal in the household and community. Systematic reviews can provide new evidence for decision making, but the approach we present is reliant on trial authors and journals adhering to agreed standards of reporting. 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