Differential Effectiveness of Water, Sanitation, and Handwashing Interventions to Reduce Child Diarrhea in Dry and Rainy Seasons: A Systematic Review and Meta-Analysis of Intervention Trials.

BACKGROUND

Studies evaluating how water, sanitation, and/or handwashing (WASH) interventions in low- and middle-income countries impact diarrheal diseases have shown inconsistent results. The prevalence of enteric pathogen infections and diarrhea are highly seasonal and climate-sensitive, which could explain heterogeneous findings. Understanding how season influences the effectiveness of WASH interventions is critical for informing intervention approaches that will be resistant under the varying weather conditions that climate change will bring.

METHODS

We conducted a systematic review of the literature and meta-analysis to test whether and to what extent the impact of WASH interventions on diarrhea differs by season. We searched the literature for randomized and nonrandomized controlled WASH intervention trials and identified the season in which data were collected-rainy, dry, or both-for each study using proximate land station weather datasets. We compared the relative risk (RR) estimates for the impact of interventions on diarrhea for each study, stratified by season, and analyzed estimates using meta-analysis and meta-regression. This study is registered with PROSPERO, CRD42021231137.

RESULTS

A total of 50 studies met the inclusion criteria, resulting in 34 drinking water intervention estimates, 8 sanitation intervention estimates, and 14 handwashing intervention estimates. Of the total studies, 60% () spanned more than one season, with most single-season studies (75%, ) occurring exclusively in the dry season. The effect of WASH interventions was stronger in dry seasons than in rainy seasons, with a 33% [95% confidence interval (CI): 24%, 41%] and 18% reduction (95% CI: 5%, 29%) in diarrhea risk, respectively. When stratified by type of intervention, the stronger effect size in dry seasons was consistent for water and handwashing interventions but not for sanitation interventions.

CONCLUSIONS

Estimates of the seasonal impact of WASH interventions revealed larger effects in the dry season than in the rainy season overall and for water and handwashing interventions in particular. These patterns likely affected previous estimates of intervention effectiveness, which included more dry season estimates. These findings suggest the need to collect data across seasons and report seasonally stratified results to allow for more accurate estimates of the burden of disease impacted by WASH investments and to improve projections of potential impacts of these interventions under future climate conditions. These findings also underscore the need for robust WASH interventions designed to be resistant to seasonal variations in temperature and rainfall now and under future climate change scenarios. https://doi.org/10.1289/EHP14502.