At Monash Medical Centre we currently use a two step algorithm to detect toxigenic Clostridium difficile. Specimens are initially screened to establish the presence of C. difficile by detecting glutamate dehydrogenase (GDH), using the C.DIFF CHEK™ -60 (Techlab) enzyme immunoassay. GDH positive samples are subsequently tested for toxigenicity using the Xpert® C. diff assay (Cepheid), a qualitative real time polymerase chain reaction (PCR) run on the GeneXpert which detects the toxin B gene, a binary toxin gene and the tcdC gene deletion at nt 117.
Other molecular based assays designed to detect toxigenic C. difficile are commercially available. Two such assays are the GeneOhmTM C. diff (Becton Dickinson), a real-time PCR which detects the presence of the toxin B gene in direct faecal samples, and the illumigene® C. difficile assay (Meridian Bioscience) which uses loop-mediated amplification technology with primers designed to amplify a region of the toxin A gene.
The aim of this investigation was to compare the performance of the GeneOhmTM C. diff and illumigene® C. difficile assays to the Xpert® C. diff assay. A total of 125 GDH positive samples were tested by all three methods, and samples with discrepant results were cultured onto ChromID C. diff agar (Biomerieux) and sent to a reference laboratory for confirmation. The GeneOhmTM C. diff and the illumigene® C. difficile assays were found to have a sensitivity of 98.7% and 80.3% respectively, with both assays having a specificity of 100%. The results of this study showed the Xpert® C. diff to have the best performance of all three assays as a method of detection for toxigenic C. difficile.