Background and Objective: The current gold standards for the diagnosis of C. difficile infection (CDI) are toxigenic culture and faecal cytotoxicity assays, both of which are time consuming and require expertise. Other detection methods used in diagnostic settings include toxin enzyme immunoassay (EIA), which has low sensitivity, and nucleic acid amplification tests (NAATs). The Becton Dickinson (BD) GeneOhm Cdiff assay is a NAAT, which has demonstrated a high sensitivity (83.6-95.5%) and specificity (97.7-99.7%). Recently, the BD MAX platform, which performs on the same principles as BD GeneOhm, has become available in Australia. As there have been limited studies of the BD MAX Cdiff assay world-wide, and none in Australia, this study aimed to investigate its sensitivity and specificity for the detection of toxigenic C. difficile in human stool samples in an Australian setting.
Methods: Between December 2013 and January 2014, 406 stool specimens from 349 patients were analysed with the BD MAXCdiff assay. Direct and enrichment toxigenic culture were performed on BioMérieux ChromID C. difficile agar as a reference method. Isolates from specimens with discrepant results were further analysed with an in-house PCR to detect the presence of toxin genes.
Results: The overall prevalence of toxigenic C. difficile was 8.9%. Concordance between the BD MAX assay and enrichment culture occurred in 98.5% of the specimens. The sensitivity, specificity, positive predictive value and negative predictive value for the BD MAX Cdiff assay were 95.5%, 99.0%, 87.5% and 99.7%, respectively, when compared to direct culture, and 91.7%, 99.0%, 88.0%, 99.4% and 94.7%, respectively, when compared to enrichment culture.
Conclusion: The new BD MAX Cdiff assay demonstrated a high sensitivity and specificity comparable to the BD GeneOhm Cdiff assay. The results indicate that BD MAX is an excellent platform for rapid and accurate detection of toxigenic C. difficile.