This study develops and applies a mechanistic transmission model to explore why WASH (Water, Sanitation, and Hygiene) interventions often produce inconsistent results across different settings. By simulating intervention trials, the researchers examined how four key factors—community coverage, compliance, intervention efficacy, and the proportion of transmission that can be blocked—interact with contextual variables such as baseline disease prevalence and existing WASH infrastructure.
Two hypothetical scenarios were modeled: one with low and one with high baseline disease prevalence. In the low-prevalence scenario, even moderate levels of coverage and compliance led to substantial health improvements. In contrast, the high-prevalence scenario required much higher levels of coverage and compliance to achieve similar reductions in disease burden.
The findings highlight that WASH intervention outcomes are non-linear and highly dependent on context and interactions between factors. Many of the null results observed in recent WASH trials may not reflect failed interventions, but rather mismatches between the intervention design and local conditions. The study demonstrates that mechanistic models can play a critical role in enhancing policy development and intervention planning by allowing program designers to simulate realistic, location-specific scenarios. This work responds to growing calls in the WASH research community for better tools to generalize trial results and inform more targeted, evidence-based decision-making.
Author(s): Brouwer, Andrew F.; Kraay, Alicia N.M.; Zahid, Mondal H.; Eisenberg, Marisa C.; Freeman, Matthew C.; Eisenberg, Joseph N.S.
Published: 2025
Language: English
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Additional Information
Diarrheal disease is a leading cause of morbidity and mortality in young children. Water, sanitation, and hygiene (WASH) improvements have historically been responsible for major public health gains, but many individual interventions have failed to consistently reduce diarrheal disease burden. Analytical tools that can estimate the potential impacts of individual WASH improvements in specific contexts would support program managers and policymakers to set targets that would yield health gains. We developed a disease transmission model to simulate an intervention trial with a single intervention. We accounted for contextual factors, including preexisting WASH conditions and baseline disease prevalence, as well as intervention WASH factors, including community coverage, compliance, efficacy, and the intervenable fraction of transmission. We illustrated the sensitivity of intervention effectiveness to the contextual and intervention factors in each of two plausible disease transmission scenarios with the same disease transmission potential and intervention effectiveness but differing baseline disease burden and contextual/intervention factors. Whether disease elimination could be achieved through a single factor depended on the values of the other factors, so that changes that could achieve disease elimination in one scenario could be ineffective in the other scenario. Community coverage interacted strongly with both the contextual and the intervention factors. For example, the positive impact of increasing intervention community coverage increased non-linearly with increasing intervention compliance. With lower baseline disease prevalence in Scenario 1 (among other differences), our models predicted substantial reductions could be achieved with relatively low coverage. In contrast, in Scenario 2, where baseline disease prevalence was higher, high coverage and compliance were necessary to achieve strong intervention effectiveness. When developing interventions, it is important to account for both contextual conditions and the intervention parameters. Our mechanistic modeling approach can provide guidance for developing locally specific policy recommendations.