Abstract
Microbiological water quality is usually assessed by the identification of Escherichia coli (E. coli), a fecal indicator. The hydrogen sulfide (H(2)S) test is an inexpensive, easy-to-use, and portable alternative field-based water quality test. Our study evaluated the H(2)S test's effectiveness as a water quality indicator for diarrhea risk. Field workers collected stored drinking water samples for H(2)S analysis and detection of E. coli by membrane filtration and measured caregiver-reported diarrhea among children < 5 years in the same households 1 month later. We assessed the association between the H(2)S test (incubated for 24 hours and 48 hours) and diarrhea prevalence, with 2-day and 7-day symptom recall periods (N = 1,348). We determined the sensitivity, specificity, and positive and negative predictive value (PPV, NPV) of the H(2)S test compared with E. coli (N = 525). Controlling for potentially confounding covariates, H(2)S-positive water (at 24 or 48 hours) was not associated with 2-day diarrhea prevalence (24-hour prevalence ratio [PR] = 1.03, 95% confidence interval [CI]: 0.63-1.69; 48-hour PR = 0.89, 95% CI: 0.58-1.38) or 7-day diarrhea prevalence (24-hour PR = 1.17, 95% CI: 0.76-1.78; 48-hour PR = 1.21, 95% CI: 0.81-1.80). The sensitivity, PPV, and NPV of the H(2)S test was significantly higher when the H(2)S test was incubated for 48 versus 24 hours whereas specificity showed the opposite trend. H(2)S test sensitivity, PPV, and NPV increased with increasing E. coli levels, consistent with previous evidence that the H(2)S test is a useful water quality tool in high-contamination settings. However, our results suggest that the H(2)S test is not an effective indicator for waterborne diarrhea.