Evaluation of enzyme immunoassays to detect Clostridium difficile toxin from anaerobic stool culture

Stool culture for Clostridium difficile, while necessary for strain typing and antimicrobial surveillance, cannot determine toxin production. We prospectively tested in triplicate 91 C difficile cultured isolates for toxin production by 2 enzyme immunoassays (EIAs) (Meridian Premier Toxins A&B, Meridian Bioscience, Cincinnati, OH; and TechLab Tox A/B II, TechLab, Blacksburg, VA) and cytotoxin neutralization bioassay (CTN). By CTN, 88% (80/91) were toxigenic. Reproducibility was 93% (85/91) for CTN, 80% (73/91) for Meridian EIA, and 79% (72/91) for TechLab EIA. Compared with CTN, sensitivities were 87.1% and 89.2% for the Meridian and TechLab EIAs, respectively. In an additional 115 stool specimens, CTN detected toxin more frequently from cultured isolates (96/115) than stool (84/115). For C difficile toxin detection from isolates, EIA was less reproducible than CTN. EIA methods can be falsely negative in 10% to 12% of isolates, and these should be tested by CTN or polymerase chain reaction. When positive, EIA is fast and reliable for detecting C difficile toxin from culture.