Abstract
Clostridium difficile infection is the primary cause of health care-associated diarrhea. While most laboratories have been using rapid antigen tests for detecting C. difficile toxins, they have poor sensitivity; newer molecular methods offer rapid results with high test sensitivity and specificity. This study was designed to compare the performances of two molecular assays (Meridian illumigene and BD GeneOhm) and two antigen assays (Wampole Quik Chek Complete and TechLab Tox A/B II) to detect toxigenic C. difficile. Fecal specimens from hospitalized patients (n = 139) suspected of having C. difficile infection were tested by the four assays. Nine specimens were positive and 109 were negative by all four methods. After discrepant analysis by toxigenic culture (n = 21), the total numbers of stool specimens classified as positive and negative for toxigenic C. difficile were 21 (15%) and 118 (85%), respectively. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were as follows: GeneOhm (95.2%, 100%, 100%, and 99.2%), illumigene (95.2%, 96.6%, 83.3%, and 99.2%), Tox A/B II (52.4%, 97.5%, 78.6%, and 92.4%), and Quik Chek Complete (47.6%, 100%, 100%, and 91.9%). The illumigene assay performed comparably to the GeneOhm assay with a slight decrease in test specificity; the sensitivities of both far exceeded those of the antigen assays. The clinical characteristics of the concordant and discrepant study patients were similar, including stool consistency and frequency. In the era of rapid molecular-based tests for toxigenic C. difficile, toxin enzyme immunoassays (EIAs) should no longer be considered the standard of care.