Melting curve analysis reveals false-positive norovirus detection in a molecular syndromic panel

Background: Molecular syndromic panels can improve rapidity of results and ease clinical laboratory workflow, although caution has been raised for potential false-positive results. Upon implementation of a new panel for infectious diarrhea (BioFire (R) FilmArray (R) Gastrointestinal [GI] Panel, bioMerieux) in our clinical laboratory, a higher than expected number of stool samples with norovirus were detected. Objectives: The goal of this study was to investigate positive percent agreement and the false-positive rate of norovirus detected by the multiplex BioFire GI panel compared to a singleplex commercial assay. Study design: From October 2023 to January 2024, all prospective stool samples with a positive norovirus result by BioFire had melting curves reviewed manually using the BioFire FilmArray Torch System. Stool samples further underwent testing by a supplementary real-time RT-PCR assay (Xpert (R) Norovirus, Cepheid) for comparative analysis. Results: Of the 50 stool samples with norovirus detected by BioFire, 18 (36 %) tested negative by Xpert (deemed "false-positives"). Furthermore, melting curve analysis revealed nearly all of these samples had atypical melting curve morphologies for the "Noro-1" target on BioFire (16/18, 89 %), which was statistically significant (Odds Ratio 173.2, 95 % CI [22.2, 5326.9], p < 0.0001). Stool samples with multiple pathogens detected by BioFire including norovirus were not more likely to produce false-positive norovirus results (Odds Ratio 1, 95 % CI [0.3, 3.3], p = 1). Conclusions: Although not described in the manufacturer's Instructions for Use, we propose routine manual review of melting curves for the BioFire GI panel prior to reporting, to mitigate potential false-positive norovirus results.