Evaluation of the illumigene C. difficile assay for toxigenic Clostridium difficile detection: a prospective study of 302 consecutive clinical fecal samples

Toxigenic Clostridium difficile is a major pathogen causing nosocomial diarrhea. Consequently, rapid detection of toxigenic C. difficile is very important in clinical laboratories. The illumigene C. difficile DNA amplification assay (illumigene; Meridian Bioscience, Inc.) is a rapid method that detects the toxin A gene (tcdA) by loop-mediated isothermal amplification. In the present study, we evaluated the diagnostic performance of the illumigene assay using 302 consecutive stool specimens in comparison with the VIDAS C. difficile A&B enzyme-linked fluorescent immunoassay (VIDAS-CDAB; bioMérieux). Toxigenic culture was used as the reference method. The sensitivity, specificity, positive predictive value, and negative predictive value of the illumigene assay were 88.1%, 96.7%, 86.7%, and 97.1%, respectively, while those of the VIDAS-CDAB assay were 40.4%, 98.8%, 87.5%, and 88.5%, respectively. It is of note that use of a combination of the illumigene and VIDAS-CDAB assays did not improve any of the 4 evaluated parameters (88.1%, 95.5%, 82.5%, and 97.1%, respectively). The illumigene assay showed limits of detection of 250 and 11,467 CFU/mL for ATCC 9688 (tcdA+, tcdB+, cdtB-) and ATCC 43598 (tcdA-, tcdB+, cdtB-) reference strains, respectively, and there was no cross-reactivity with 8 frequently isolated bacterial species. In conclusion, the illumigene assay might be a useful method for rapid detection of toxigenic C. difficile in clinical laboratories. Additionally, the VIDAS-CDAB assay seems unnecessary if the illumigene assay is used.