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Comparison of SARS-CoV-2 detection with the Cobas® 6800/8800 system on gargle samples using two sample processing
Patrick Benoit1, Annie-Claude Labbé1,2, Linda Lalancette3
1Département de microbiologie, Infectiologie et Immunologie, Université de Montréal, Québec, Canada.
Background:
Gargle samples have been proposed as a noninvasive method for detection of SARS-CoV-2 RNA. The clinical performance of gargle specimens diluted in Cobas® PCR Media and in Cobas® Omni Lysis Reagent was compared to oropharyngeal/nasopharyngeal swab (ONPS) for the detection of SARS-CoV-2 RNA.
Study Design:
Participants were recruited prospectively in two COVID-19 screening clinics. In addition to the ONPS, participants gargled with 5 ml of natural spring water split in the laboratory as follows: 1 ml was added to 4.3 ml of polymerase chain reaction (PCR) media and 400 μl was added to 200 μl of lysis buffer. Testing was performed with the Cobas® SARS-CoV-2 test on the Cobas® 6800 or 8800 platforms.
Results:
Overall, 134/647 (20.7%) participants were considered infected because the ONPS or at least one gargle test was positive. ONPS had, respectively, a sensitivity of 96.3% (95% confidence interval [CI]: 91.3-98.5); both gargle processing methods were slightly less but equally sensitive (90.3% [95% CI: 83.9-94.3]). When ONPS and gargle specimens were both positive, the mean cycle threshold (Ct ) was significantly higher for gargles, suggesting lower viral loads.
Conclusion:
Gargle specimens directly added in PCR Media provide a similar clinical sensitivity to chemical lysis, both having a slightly, not significantly, lower sensitivity to ONPS.
