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. However, current estimates of the health impacts of WASH improvements use self-reported morbidity, which may fail to capture longer-term or more severe impacts. Moreover, reported mortality is thought to be less prone to bias. This study aimed to answer the question: what are the impacts of WASH intervention improvements 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 trials of WASH improvements implemented under endemic disease conditions in L&MICs were eligible, from studies 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 non-randomized 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 improvements are associated with a significant reduction of 17 percent 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 percent (OR=0.55, 95%CI=0.35, 0.84; 10 interventions). Further analysis by WASH technology suggested 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 main components of 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.