The study developed a mechanistic susceptible–infectious–susceptible (SIS) transmission model calibrated using Bayesian sampling and maximum-likelihood techniques to fit data from the WASH Benefits Bangladesh randomized trial of over 17,000 observations. The investigators simulated counterfactual scenarios that varied contextual and intervention parameters such as preexisting WASH conditions, baseline disease burden, intervention compliance, efficacy, coverage, and the proportion of transmission pathways left unmodified. Results indicated that increasing community-level intervention coverage from approximately 5% (typical in trials) to 20% led to dramatic gains in effectiveness—median improvements of around 34 percentage points for WSH and 45 percentage points when nutrition was added. The effectiveness of interventions was significantly reduced in contexts with poorer baseline WASH infrastructure or higher initial disease prevalence. Combined interventions provided complementary benefits, though not synergistic interactions. The authors conclude that individual-level WASH strategies, even when implemented with high fidelity, are unlikely to deliver meaningful health improvements unless community coverage reaches levels sufficient to disrupt pathogen transmission—akin to herd protection.
Author(s): Brouwer, Andrew F.; Zahid, Mondal H.;
Eisenberg, Marisa C.;
Arnold, Benjamin F.;
Ashraf, Sania;
Benjamin-Chung, Jade;
Colford, John M. Jr.;
Ercumen, Ayse;
Luby, Stephen P.;
Pickering, Amy J.;
Rahman, Mahbubur;
Kraay, Alicia N.M.;
Eisenberg, Joseph N.S.;
Freeman, Matthew C.
Published: 2024
Language: English
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Additional Information
The authors re‑analyzed the WASH Benefits Bangladesh trial using a mechanistic counterfactual simulation model to explore why large‑scale WASH interventions often failed to deliver expected health impacts, especially reductions in childhood diarrhea and stunting. By fitting a transmission model to trial data and simulating variations in community-level coverage, pre-existing WASH conditions, intervention compliance, and environmental transmission pathways, they found that higher community coverage dramatically increases intervention effectiveness. Individual-level measures had limited impact unless near-threshold coverage for herd protection was achieved. These findings emphasize the need for community-wide strategies and interventions that address transmission routes beyond traditional water, sanitation, and hygiene channels.