Comparison of SARS-CoV-2 detection from combined nasopharyngeal/oropharyngeal swab samples by a laboratory-developed real-time RT-PCR test and the Roche SARS-CoV-2 assay on a cobas 8800 instrument

Boutin, Catherine-Audrey; Grandjean-Lapierre, Simon; Gagnon, Simon; Labbé, Annie-Claude; Charest, Hugues; Roger, Michel; Coutlée, François

OBJECTIVE: Although several assays have been developed to detect SARS-CoV-2 RNA in clinical specimens, their relative performance is unknown. METHODS: The concordance between the cobas 8800 SARS-CoV-2 and a laboratory developed (LD) reverse transcriptase-polymerase chain reaction (RT-PCR) assay was assessed on 377 combined nasopharyngeal/oropharyngeal swabs in Hanks medium. RESULTS: The positive and negative agreement between these assays were 99.3 % (95 % CI, 97.3–99.9) and 77.1 % (95 % CI, 67.7–84.4), respectively, for an overall agreement of 93.6 % (95 % CI, 90.7–95.7) beyond random chance (kappa of 0.82, 95 % CI, 0.75−0.85). Of the 22 samples positive by cobas SARS-CoV-2 only, 9 were positive only for ORF-1 gene and had Cycle thresholds (Ct) > 35.1, 8 were positive only for the E gene with Ct > 35.5 and 5 were positive for both targets with Ct > 33.9. Samples positive only with the cobas assay were more often positive with only one gene target (77.3 %) than samples positive in both assays (16.9 %, p < 0.0001). Ct values in the cobas SARS-CoV-2 assay were significantly higher in the 279 samples testing positive in both assays (32.9 %, 95 % CI 32.3–33.6) compared to the 22 samples with discordant results (36.6 %, 95 % CI 36.2–37.1; p = 0.0009). An excellent correlation (r(2) = 0.98) was obtained between Ct values of the ORF-1 and E targets in the cobas assays and a good correlation was obtained between LD RT-PCR test and cobas SARS CoV-2 ORF-1 target (r(2) = 0.82). CONCLUSION: Our study demonstrated an excellent concordance between a LD RT-PCR and the cobas SARS-CoV-2 tests on the 8800 platform.