Comparison of a rapid molecular method, the BD GeneOhm Cdiff assay, to the most frequently used laboratory tests for detection of toxin-producing Clostridium difficile in diarrheal feces.

Six hundred diarrheal stool specimens were collected from inpatients and outpatients at local university hospitals for the detection of toxigenic Clostridium difficile using three parallel methods, the BD GeneOhm Cdiff assay, the tissue culture cytotoxicity assay, and a commercially available enzyme-linked fluorescence immunoassay (ELFA) (Vidas C. difficile toxin A and B assay; bioMérieux). Toxigenic C. difficile culture was also performed to further clarify discordant results. During a 3-month study period, 58 (9.7%) of the 600 diarrheal samples examined were positive by the BD GeneOhm Cdiff assay, while the Vidas C. difficile toxin A and B assay and the cytotoxicity assay performed directly on stool samples gave 4.7% and 6.3% positivity rates, respectively. In the case of four samples, BD GeneOhm Cdiff assay results were not evaluable at first because of the presence of PCR inhibitors, but upon repeat testing from the frozen lysates, all of these samples proved to be negative. After resolution with toxigenic culture, the cytotoxicity assay proved to be positive in 55 samples (9.2%), while the ELFA was positive in 37 samples (6.2%). Results of culture and repeated cytotoxicity assays emphasized the importance of the culture method, because the use of ELFA or enzyme immunoassay without a culture method may lead to a substantial portion of toxigenic C. difficile strains being missed.