Xpert norovirus

The GXP four module system and the proprietary analysis kits were used throughout this study; Xpert® C.difficile BT (GXCDIFFBT-CE-10), Xpert® Norovirus (GXNOV-CE-10) and Xpress Xpert® Flu/RSV (XPRSFLU/RSV-CE-10, Cepheid UK Ltd Woburn Green, England). The Cepheid SOP was adhered to.
The only deviation was to use different specimen collection equipment. This meant that dry rayon tipped swabs (Medical Wire, Bath England, MW118S) were used for processing faeces and vomit.
Raw unformed stool specimens and vomit were collected in a sterile universal container, free from any additives. Specimens were stored at 2-8°C when necessary for up to 48h. Stool samples were processed using a seasonal priority algorithm; between October and March they were processed for NV and then, if negative, CD. From April to September the converse occurred, stool samples were analysed for CD and then, if negative, NV. The only deviation from this was when particular patient samples were flagged as part of a possible outbreak of NV. This algorithm helped maximise module availability and speed of sample processing. We operated a five day service, Monday to Friday from 9am -5.30pm.

We compared 2 different approaches during the study period. The first approach was a standard approach that was historically implemented and included Nv or Cd testing only at the request of clinicians or infection control practitioners using an immunochromatographic test (ICT) (RidaQuick Norovirus; R-Biopharm, Darmstadt, Germany) or a PCR assay (Xpert C. difficile; Cepheid, Sunnyvale, CA) within a 1-hour turnaround time (TAT).
The second approach was a new 2-step laboratory-based approach using PCR assays: Nv were tested on the initiative of the laboratory on each Cd negative stool specimen using a new PCR assay according to the manufacturer's recommendations. This new molecular assay (Xpert Norovirus; Cepheid) detects the 2 main human genogroups (GI and GII) over 90 minutes. These 2 approaches were tested simultaneously during the same period to limit confounding factors. The result of each test was immediately transmitted to the infection control team to verify the implementation of precautions measures. Only 1 episode per patient was included. Patients were informed, and consent was obtained.