Comparison of BD MAX Check-Points CPO assay with Cepheid Xpert Carba-R assay for the detection of carbapenemase-producing Enterobacteriaceae directly from rectal swabs

We compared the performance of 2 automated systems for detection of carbapenemase-producing Enterobacteriaceae, BD MAX Check-Points CPO (CPO assay) and Xpert Carba-R assay, with culture confirmed by polymerase chain reaction as the reference method. Using 867 samples from 627 patients, the overall sensitivity, specificity, total positive predictive value, and negative predictive value of the CPO assay were 95.7%, 96.5%, 60.8% and 99.8% and for the Xpert assay were 97.9%, 99.8%, 95.8%, and 99.9%, respectively. The cycle threshold values (Ct value) of the false-positive CPO assay results were significantly higher than those of true-positive cases (P < 0.001). By applying a modified cut-off Ct value of 37.3 for klebsiella pneumoniae carbapenemases (KPC), the positive predictive value for KPC was improved from 52.9% to 89.5%. The CPO assay will be useful when handling many specimens, as tests are conducted in batches. However, positive cases showing high Ct values should be confirmed by another assay to rule out false positivity.