Comparison of Two Rapid Assays for Clostridium difficile Common Antigen and a C difficile Toxin A/B Assay With the Cell Culture Neutralization Assay

We compared 3 rapid assays for Clostridium difficile with a cell culture cytotoxicity neutralization assay (CCNA). Of 600 stool samples, 46 were positive for toxigenic C difficile. Both rapid common antigen assays were highly sensitive (91.3%-100%) and, therefore, were appropriate screening tests The rapid toxin assay had poor sensitivity (61%) but excellent specificity (99 3%) Testing stools for glutamate dyhydrogenase (step 1) and those positive with a rapid toxin assay (step 2) would correctly classify 81% of submitted specimens within 2 hours, including during periods of limited staffing (evenings, nights, and weekends). CCNA could then be used as a third step to test rapid toxin-negative samples, thereby providing a final result for the remaining 19% of samples by 48 to 72 hours The use of rapid assays as outlined could enhance timely diagnosis of C difficile.