Background: Sustained investment in water, sanitation and hygiene (WASH) has lagged in resource-poor settings; incremental WASH improvements may, nonetheless, prevent diseases such as typhoid in disease-endemic populations.
Methods: Using prospective data from a large cohort in urban Kolkata, India, we evaluated whether baseline WASH variables predicted typhoid risk in a training subpopulation (n=28470). We applied a machine learning algorithm to the training subset to create a composite, dichotomous (“good”, “not good”) WASH variable based on four variables and evaluated sensitivity and specificity of this variable in a validation subset (n=28470). We evaluated in Cox regression models whether residents of “good” WASH households experienced lower typhoid risk after controlling for potential confounders. We constructed virtual clusters (radius 50m) surrounding each household to evaluate whether “good” WASH prevalence modified typhoid risk in central household members.
Results: “Good” WASH was associated with protection in analyses of all households (Hazard ratio (HR)=0.57, 95% CI: 0.37-0.90, p=0.015). This protection was evident in persons ≥5 years at baseline (HR=0.47, 95% CI: 0.34-0.93, p=0.005) and was suggestive, though not statistically significant, in younger age groups (HR=0.61, 95% CI: 0.27-1.38, p=0.235). The level of surrounding household “good” WASH coverage was also associated with protection (HR=0.988, 95% CI: 0.979-0.996, p=0.004, for each percent coverage increase). However, collinearity between household WASH and WASH coverage prevented assessment of their independent predictive contributions.
Conclusion: In this typhoid-endemic setting, natural variation in household WASH was associated with typhoid risk. If replicated elsewhere, these findings suggest that WASH improvements short of major infrastructural investments may enhance typhoid control.
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