Evaluation of four methods for detection of Clostridium difficile or C. difficile toxin: cytotoxin assay, culture, latex agglutination, and a new rapid immunoassay (C. difficile toxin A test).

The performance of C. difficile toxin A test (Oxoid, Basingstoke, UK), an immunoassay for the detection of C. difficile toxin A in fecal samples, for the diagnosis of C. difficile-associated diarrhea was compared with those of cytotoxin assay, culture, and a latex agglutination assay (Culturette Brand CDT Rapid Clostridium difficile test; Becton Dickinson, Cockeysville, MD). A total of 105 stool specimens from 71 patients were tested. Of the 105 specimens analyzed, 6 (5.7%) samples were positive by all four methods, 66 samples (62.9%) were concordant negative. Two patients fulfilled all clinical criteria for C. difficile-associated diarrhea but had negative results in the cytotoxicity tests. The sensitivity and specificity, as determined against cytotoxin assay results, were, respectively 52.4% and 93.9% for latex agglutination, 68.2% and 84.3% for rapid immunoassay and 36.4% and 92.8% for culture. No single laboratory test yields a definitive diagnosis of C. difficile-associated diarrhea at present. Test results by any of these methods must be used in conjunction with patient history when making the diagnosis to avoid indiscriminate treatment of individuals without disease or the lack of treatment for individuals with a serious infection. We consider the rapid and easy-to-perform C. difficile toxin A test not to be an essential adjunct for the diagnosis of C. difficile-associated diarrhea.