The H(2)S test versus standard indicator bacteria tests for faecal contamination of water: systematic review and meta-analysis.

OBJECTIVES: To assess the diagnostic accuracy of the H(2)S test for microbiological contamination of domestic water across different settings, as a basis for providing guidance on its use.
METHODS: We searched a range of bibliographic and 'grey' literature databases to identify studies that had processed domestic water samples using both the H(2)S test and recognized tests for thermotolerant coliforms or Escherichia coli. We screened 661 study abstracts and identified 51 relevant studies based on 13 853 water samples. For each relevant study, we recorded the level of correspondence between the H(2)S and recognized tests, microbial testing procedures, details of the samples processed and study quality indicators. We conducted a meta-analysis to investigate the impact of testing procedures, study quality and sample characteristics on the diagnostic accuracy of the H(2)S test.
RESULTS: H(2)S test implementation varied between studies, and the test's diagnostic accuracy varied significantly and substantially between studies. Little of this variation was explained by testing procedures, study quality or the nature of the samples processed.
CONCLUSIONS: Although in widespread use, our findings suggest that the diagnostic accuracy, particularly specificity, of the H(2)S test is variable. Optimal conditions for conducting the test remain unclear. As H(2)S test accuracy is low in a minority of these studies, we recommend that its performance be evaluated relative to standard methods, prior to its operational deployment in a new setting.