Comparative performance of the GeneXpert C. difficile PCR assay and C. diff Quik Chek Complete kit assay for detection of Clostridium difficile antigen and toxins in symptomatic community-onset infections

• Non-repetitive 409 stools were tested simultaneously by GeneXpert, QCC and TC.
• 19 out of 409 samples were positive for GDH, in stool and CMB by the QCC.
• 7 out of 409 were positive for both GDH and toxins A/B by the QCC.
• GeneXpert was more sensitive than QCC for detection of C. difficile toxin in stool.
• Both GeneXpert and QCC assays were highly specific.

SummaryObjectivesTo evaluate the performance of the GeneXpert C. difficile assay and C. diff Quik Chek Complete (QCC) kit for the detection of toxins from fecal specimens and cooked meat broth (CMB) culture using toxigenic stool culture as reference method, for the diagnosis of C. difficile infection (CDI) in a community setting.MethodsNon-repeat stool samples were tested simultaneously by GeneXpert and QCC. Toxin detection was done on neat stool samples, inoculated CMB, and isolated colonies.ResultsNineteen (4.6%) of 409 samples were positive for glutamate dehydrogenase (GDH) in stool and CMB by the QCC assay; seven (1.7%) were positive for both GDH and toxins A/B. The sensitivities of QCC to detect C. difficile toxin directly in stool specimens and CMB were 68.4% and 100%, respectively, while specificities were 100% and 83%, respectively. C. difficile toxin was detected in 10 (2.5%) specimens and 13 (3.2%) CMB. Thirteen (68.4%) of 19 isolates were positive for C. difficile toxin by GeneXpert and QCC and were taken as the reference toxigenic culture. The disease burden was thus 3.2%. The sensitivities of GeneXpert in stool and CMB were 81.3% and 100%, respectively, while specificities were 100% and 100%, respectively.ConclusionThe GeneXpert assay was more sensitive than QCC for the detection of C. difficile toxin in stool, but both assays were highly specific.