The H2S test versus standard indicator bacteria tests for faecal contamination of water: systematic review and meta-analysis

Objectives To assess the diagnostic accuracy of the H2S 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 H2S 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 H2S 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 H2S test.

results H2S 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 H2S test is variable. Optimal conditions for conducting the test remain unclear. As H2S 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.