Abstract
Water, sanitation, and handwashing interventions may confer spillover effects on intervention recipients’ neighbors by interrupting pathogen transmission. We measured geographically local spillovers in the Water Quality, Sanitation, and Handwashing (WASH) Benefits Study, a cluster-randomized trial in rural Bangladesh, by comparing outcomes among neighbors of intervention versus those of control participants. Geographically defined clusters were randomly allocated to a compound-level intervention (i.e., chlorinated drinking water, upgraded sanitation, and handwashing promotion) or control arm. From January 2015 to August 2015, in 180 clusters, we enrolled 1,799 neighboring children who were age matched to trial participants who would have been eligible for the study had they been conceived slightly earlier or later. After 28 months of intervention, we quantified fecal indicator bacteria in toy rinse and drinking water samples and measured soil-transmitted helminth infections and caregiver-reported diarrhea and respiratory illness. Neighbors’ characteristics were balanced across arms. Detectable Escherichia coli prevalence in tubewell samples was lower for intervention participants’ neighbors than control participants’ (prevalence ratio = 0.83; 95% confidence interval: 0.73, 0.95). Fecal indicator bacteria prevalence did not differ between arms for other environmental samples. Prevalence was similar in neighbors of intervention participants versus those of control participants for soil-transmitted helminth infection, diarrhea, and respiratory illness. A compound-level water, sanitation, and handwashing intervention reduced neighbors’ tubewell water contamination but did not affect neighboring children’s health.
Highlights
Improvements in household water quality, handwashing practices, and sanitation (WSH)may reduce the risk diarrhea,[1] soil-transmitted helminth (STH) infection[2] and respiratory illness.[3,4] WSH interventions may reduce illness among neighbors through “spillover effects”[5] (a.k.a. “herd effects”[6,7,8] or “indirect effects”9) through 1) reduced fecal contamination in the environment surrounding intervention recipients, 2) reduced pathogen transmission from intervention recipients to neighbors, or 3) adoption of promoted health behaviors by neighbors
Disease prevalence was similar in neighbors of intervention vs. control participants: Ascaris, hookworm (PD=0.01; -0.01, 0.04), Trichuris (PD=0.02; -0.02, 0.05), diarrhea (PD=0.00; -0.02, 0.03), respiratory illness (PD=-0.01; -0.04, 0.03)
We conducted a randomized trial in rural Bangladesh to measure whether neighbors of a compound-level WSH intervention improved hygiene behaviors and had lower prevalence environmental contamination, soil-transmitted helminth infection, diarrhea, and respiratory illness among children under 5 years after two years of intervention
Summary
Improvements in household water quality, handwashing practices, and sanitation (WSH)may reduce the risk diarrhea,[1] soil-transmitted helminth (STH) infection[2] and respiratory illness.[3,4] WSH interventions may reduce illness among neighbors through “spillover effects”[5] (a.k.a. “herd effects”[6,7,8] or “indirect effects”9) through 1) reduced fecal contamination in the environment surrounding intervention recipients, 2) reduced pathogen transmission from intervention recipients to neighbors, or 3) adoption of promoted health behaviors by neighbors. If WSH interventions reduce illness among both recipients and other individuals, intervention effect estimates that ignore spillover effects will be underestimated. There is a rich literature on herd effects of vaccines.[5,7] The literature on spillover effects for other infectious disease interventions, such as school-based deworming[10] and insecticide treated nets,[11] is growing.[5] While many empirical studies have measured WSH interventions’ effects directly on recipients,[1,2,3] few have measured spillover effects of WSH;[12,13,14,15,16,17,18,19] these studies used observational designs to measure spillovers, so spillover estimates may be susceptible to bias if there are systematic differences between individuals in close proximity to intervention and individuals serving as controls
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