A Randomized Controlled Trial to Measure Spillover Effects of a Combined Water, Sanitation, and Handwashing Intervention in Rural Bangladesh

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.

Figure 1.

Theoretical model for spillover effects of a compound-level combined water, sanitation, and handwashing intervention in the Water Quality, Sanitation, and Handwashing (WASH) Benefits Study, January 2015–August 2015. Contamination of neighbors’ water source and stored water was measured by enumerating fecal indicator bacteria in drinking-water samples. Fecal contamination of the neighbors’ compound and environment was measured by counting synanthropic flies captured near cooking areas and latrines. Contamination of hands in the neighbors’ compound environment was measured by observing caregiver’s and children’s hand cleanliness. Upward arrows indicate increases; downward arrows indicate decreases. STH, soil-transmitted helminth.

Figure 2.

Design of Water Quality, Sanitation, and Handwashing (WASH) Benefits Study, January 2015–August 2015. This figure depicts the study design in 2 clusters: 1 assigned to the combined WSH intervention and the other assigned to control. Each cluster was separated by a buffer zone of at least 1 km to minimize the chance of spillovers between clusters. The numbered circles denote the compounds enrolled in the WASH Benefits Study. The gray diamonds denote the neighboring compounds enrolled in the spillover study. The boundaries of each cluster were not formally defined in the WASH Benefits Study. In this figure, the darker-shaded center of each cluster is the polygon formed by linking the outermost compounds in each cluster, and the lighter-shaded section is the periphery around this polygon. We restricted enrollment to the compounds within this periphery to ensure that the 1 km buffer zone was maintained in this study. WSH, water, sanitation, handwashing.

Figure 3.

Participant flowchart, Water Quality, Sanitation, and Handwashing Benefits Study, January 2015–August 2015.

Figure 4.

Water, sanitation, handwashing intervention uptake indicators among Water Quality, Sanitation, and Handwashing Benefits Study and spillover study participants, January 2015–August 2015. Improved water quality indicators: A) participant reported treating water yesterday or B) fieldworker observed stored drinking water in the participant’s compound. Improved sanitation indicators: fieldworker observed C) participant had access to a latrine with a functional water seal or D) no visible feces on the participant’s latrine slab or floor. Improved handwashing indicators: fieldworker observed E) a participant had a handwashing location with soap or F) no visible dirt on study child’s hands or fingernails. Circles and diamonds indicate percentage of participants. Vertical lines through each circle and diamond indicate 95% confidence intervals.

Figure 5.

Unadjusted prevalence differences for the intervention versus control arms between intervention recipients and their neighbors, Water Quality, Sanitation, and Handwashing Benefits Study, January 2015–August 2015. In the main trial, soil-transmitted helminth infection was measured among index children, preschool age children, and school-aged children; diarrhea was measured among children younger than 36 months in the compound at enrollment; and respiratory illness was measured among index children and all other children younger than 5 years in the compound 2 years after the intervention. In the spillover study, all health outcomes were measured among children 0–5 years of age. Circles and triangles indicate unadjusted prevalence differences. Vertical lines through each circle and triangle indicate 95% confidence intervals.