High incidence of false positives by a latex agglutination test for the diagnosis of Clostridium difficile associated colitis in compromised patients

Detection of Clostridium difficile cytotoxin using cell culture assays for the diagnosis of antibiotic-associated colitis has been used for over a decade. Because the methodology is time consuming and cumbersome, a recently introduced commercial latex agglutination (LA) kit has attracted much attention. We compared the sensitivity and specificity of this method with the cytotoxic assay (CTA) using diarrheal stools from 652 patients at a referral tertiary care center. Specimens from 71 (10.9%) patients were found positive with CTA and 98 (15%) by LA. Of these, 67 stools were positive by both methods. Four specimens showed cytotoxicity but were negative by LA. Of the 31 patient specimens that were positive by LA but negative by CTA, 22 were obtained from leukemic bone marrow transplant and four from renal transplant patients [corrected]. Sixteen of these patients had Giardia lamblia (four), Salmonella enteritidis (three), Blastocystis hominis (five), Rotavirus (two), and Shigella boydii (two) in their stools [corrected]. No significant organisms were found in the rest of the LA-positive and CTA-negative specimens.