Comparison of culture cytotoxin assay and two EIA tests with clinical diagnosis of Clostridium difficile-associated diarrhea

Objective: The most common etiology of infectious diarrhea in hospitalized patients is Clostridium difficile. No single laboratory test yields a definitive diagnosis. Four methods were evaluated for their sensitivity and specificity in patients who had clinically defined C difficile-associated diarrhea. Methods: Clinical criteria for C difficile-associated diarrhea were defined. All adult in-hospital patients whose stools were tested for C difficile were prospectively followed. Stools were examined with culture on a selective medium, a commercial cytotoxicity assay (CTA), and two commercially available enzyme immunoassays (EIAs) for toxin A (Meridian) and toxin AB (CBC). Results: During the study period 235 stool specimens from 185 patients were tested. Fifty-one patients were positive for C difficile or its markers. CTA was most sensitive (80%), whereas CBC-EIA was most specific (98%). Differences in the sensitivities of CTA and Meridian-EIA were minor (80% versus 73.3%) and they were equally specific (95.5%). Conclusions: The sensitivity and specificity of EIA for toxin A is similar to other tests. However, due to rapidity and ease of performance, it may be a more practical test for the diagnosis of C difficile-associated diarrhea, especially if the cytotoxin assay is not available.