Effectiveness of the Hydrogen Sulfide Test as a Water Quality Indicator for Diarrhea Risk in Rural Bangladesh

Abstract

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.