Discontinuous counterimmunoelectrophoresis (DOE) was employed to detect the toxin of Clostridium difficile, etiologic antibiotic-associated colitis (AAC), in bacteria-free stool filtrates from 51 patients with diarrhea. Stool samples from 31 patients contained C. difficile toxin as determined by tissue-culture assay. A positive result was obtained by DCIE in 20 of the 31 patients (65%) and was influenced by the titer of toxin present. When toxin was present by tissue-culture assay in a dilution of 10-2 (11 samples), DCIE was positive in only 2 (18%). However, DCIE yielded positive results in 18 of the 20 samples (90%) containing toxin titers ≥10-3. The combination of DCIE and sigmoidoscopy or colonoscopy was superior to either alone in the diagnosis of AAC irrespective of the toxin titer. Nine of 11 patients (82%) whose stool samples contained C. difficile toxin in a dilution of ≥10-2 were recognized by DCIE, endoscopy, or both. In stool samples containing toxin in titers ≥10-3, no falsenegative results were encountered (sensitivity = 100%). Thus, 29 of 31 patients whose stool samples contained C. difficile toxin were identified when the results of DCIE and endoscopical examination were combined (sensitivity 93.5%). Neither endoscopical examination nor DCIE yielded positive results in the 20 patients whose stool samples lacked C. difficile toxin (specificity = 100%). DCIE is a rapid, moderately sensitive, and specific method for detecting C. difficile toxin. When DCIE is combined with endoscopy, the vast majority of patients requiring specific therapy for AAC can be identified.
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