Microbiological water quality is usually assessed by the identification of Escherichia coli (E. coli), a fecal
indicator. The
hydrogen sulfide (H2S) test is an inexpensive, easy-to-use, and portable alternative field-based water quality test. Our study evaluated the H2S test's effectiveness as a water quality
indicator for
diarrhea risk. Field workers collected stored
drinking water samples for H2S 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 H2S 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 H2S test compared with E. coli (N = 525). Controlling for potentially confounding covariates, H2S-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 H2S test was significantly higher when the H2S test was incubated for 48 versus 24 hours whereas specificity showed the opposite trend. H2S test sensitivity, PPV, and NPV increased with increasing E. coli levels, consistent with previous evidence that the H2S test is a useful water quality tool in high-contamination settings. However, our results suggest that the H2S test is not an effective
indicator for waterborne
diarrhea.