Detection of Clostridium difficile antigen and toxin in stool specimens: Comparison of the C. difficile quik chek complete enzyme immunoassay and GeneXpert C. difficile polymerase chain reaction assay

BACKGROUND/AIMS: Accurate and rapid laboratory diagnosis of Clostridium difficile infections (CDI) remains a significant challenge. A two-step algorithm for detection of toxigenic C. difficile in stool based on initial screening for glutamate dehydrogenase assay followed by confirmation by toxin A+B detection using an enzyme immunoassay (EIA) or molecular assay has been proposed. We aimed to evaluate the C. difficile Quik Chek Complete(®) (QCC-EIA) versus the GeneXpert(®) C. difficile polymerase chain reaction (PCR) assay in this two-step algorithm. MATERIALS AND METHODS: Two hundred and ten liquid stool samples obtained between June 2014 and June 2015 from patients suspected of CDI were tested by the QCC-EIA and GeneXpert PCR assay. The GeneXpert assay was used as the reference standard to calculate the QCC-EIA sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). RESULTS: Of the 210 stool samples tested, 43 (20.5%) were positive by QCC-EIA, while 31 (14.8%) were positive by GeneXpert assay. The sensitivity and specificity of the QCC-EIA were found to be 100 and 93%, respectively; the PPV and NPV were 72 and 100%, respectively. The binary toxin was detected in 12 (38.7%) and tcdC gene deletion in 3 (9.6%). CONCLUSIONS: The low specificity of QCC-EIA makes it less reliable as a confirmatory test for CDI diagnosis. This test may be used as a screening test in a two-step algorithm when combined with a molecular assay or another confirmatory test.