Background: The most reliable and accurate diagnostic method of Clostridium difficile-associated disease (CAD) is considered the detection of toxin B in stool using the cell culture cytotoxicity assay. But cytotoxicity assay needs cell culture facilities and labor intensive. We evaluated an automated enzyme-linked fluorescent immunoassay for the detection of Clostridium difficile (C. difficile) toxin A in stool specimens.

Methods: Two hundred sixty-seven stool specimens were cultured anaerobically on cycloserine-cefoxitin-fructose-egg yolk (CCFA) media and tested for toxin A with the VIDAS C. difficile toxin A II (CDA 2, bioMerieux sa, France) according to the manufacturer’s instruction. Cytotoxicity assay for toxin B (C. difficile Tox-B test, TechLab, Blacksburg, USA) was performed with 42 toxin A positive and 40 toxin A negative specimens using HEp-2 cell monolayers grown in the 96-well microplates.

Results: Toxin A positive rate (26.2%) was significantly higher (P=0.013) than the culture positive (17.6%) and the agreement was 82.4%. The agreement between the toxin A test and the cytotoxicity assay was 92.7%. The sensitivity and specificity of toxin A test were 89.4% and 100%, respectively. All the 42 toxin A positives showed cytotoxicity, but among the 40 toxin A negatives, 5 showed cytotoxicity in cell monolayers.

Conclusion: There was no significant difference between the automated, rapid toxin A test and cytotoxicity assay (P=0.07>0.05), so rapid toxin A test could be used as a routine method. However, toxin A negative and toxin B positive C. difficile would not be detected by the toxin A test only. (Korean J Clin Microbiol 2000;3(1):43-47)