Performance evaluation of Cepheid Xpert Norovirus kit with a user-modified protocol

The Cepheid Xpert® Norovirus kit automates sample processing, nucleic acid extraction, and real-time reverse transcription polymerase chain reactions (RT-PCRs) to detect norovirus genogroups I (GI) and II (GII). Eighty-five stool samples collected between February 2015 and May 2017 were used to compare the performance of a user-modified Xpert assay against a clinically validated laboratory-developed test (LDT). Of the 85 samples, 54 were previously archived in -80°C freezer. The remaining 31 were fresh samples tested concurrently with the LDT. The results of all samples tested using the Xpert kit and LDT were found to be concordant, including 12 GI- and 42 GII-positive samples, 1 GI and GII coinfection, and 30 negative samples. Comparison of the assays showed perfect concordance with a kappa coefficient score of 1.00 (95%CI from 1.00 to 1.00). Of the 30 negative stool samples tested, three samples were positive for rotavirus detected using an immunochromatographic assay, with no cross-reactivity shown in both LDT and Xpert assays. In-run sample processing control of the Xpert assay for all negative samples tested showed no/minor inhibition. Compared to the LDT, the Xpert assay produced similar or better Ct values for detection. It also showed better mitigation of PCR inhibition in stool sample testing.