SHOULD LABORATORIES TEST FOR TOXIN A-NEGATIVE, TOXIN B-POSITIVE CLOSTRIDIUM-DIFFICILE

We evaluated 300 stool specimens from patients suspected of having Clo stridium difficile-associated diarrhea to determine the prevalence of toxin A-negative, toxin B-positive C difficile isolates. Each specimen was cultured anaerobically on selective media using the heat-shock me thod and screened for C difficile toxins by two enzyme immunoassays-on e that uses an anti-toxin A monoclonal antibody and one that uses a mi xture of an anti-toxin A and an anti-toxin B monoclonal. The C diffici le strains isolated from specimens were retested for production of tox in B by a tissue culture assay and for production of toxin A by a seco nd toxin A immunoassay. Thirty-two specimens were positive and 234 spe cimens were negative for all assays. Thirty-four specimens had discrep ant results. After discrepancy analysis, all of the isolated difficile strains were determined to be either nontoxigenic (producing neither of the toxins) or toxigenic (producing both toxins). These data indica te that the prevalence of toxin A-negative, toxin B-positive strains o f C difficile is not of concern in routine diagnostic testing for C di fficile toxins in our study population.