Direct Saliva versus Conventional Nasopharyngeal Swab qRT-PCR to Diagnose SARS – CoV2: Validity Study

Background: Saliva has been demonstrated as a feasible alternative specimen to nasopharyngeal swab for the detection of SARS-CoV-2 using real-time or quantitative reverse transcription polymerase chain reaction (qRT-PCR) method that bypasses the need for explicit viral ribonucleic acid (RNA) extraction.

Aim: To assess the diagnostic validity of direct saliva-to-qRT-PCR in the detection of SARS-CoV-2 compared to conventional nasopharyngeal swab qRT-PCR.

Methodology: Self-collected saliva samples were processed by heating at 95oC for 30 minutes followed by addition of buffer and detergent while viral RNA from nasopharyngeal swabs were extracted using the Sansure Biotech sample release reagent. Paired samples were used as templates for qRT-PCR using the Sansure Novel Coronavirus (COVID-19) Nucleic Acid Diagnostic Kit and Sansure Biotech MA6000 Real-Time Quantitative PCR System. Direct saliva-to-qRT-PCR was compared to nasopharyngeal swab qRT-PCR in terms of diagnostic validity and agreement parameters, and both platforms were compared separately in terms of similar parameters with a composite reference standard (CRS) wherein the criteria for a positive result is SARS-CoV-2 detection in at least either nasopharyngeal swab or saliva.

Results: Of the 238 nasopharyngeal swab-saliva pairs tested, 20 (8.4%) nasopharyngeal swab and 24 (10.1%) saliva specimens tested positive. We documented a sensitivity of 85.0% (95% CI: 62.1%, 96.8%), specificity of 96.8% (95% CI: 93.5%, 98.7%), accuracy of 95.8% (95% CI: 92.4%, 98.0%) and Cohen Kappa of 0.75 (95% CI: 0.60, 0.90) when direct saliva-to-qRT-PCR was compared to the conventional platform. When the two platforms were individually compared to the CRS, numerically higher but not statistically significant sensitivity and accuracy were noted for direct saliva-to-qRT-PCR than for nasopharyngeal swab qRT-PCR.

Conclusion: Direct saliva-to-qRT-PCR is non-inferior to nasopharyngeal swab qRT-PCR for detecting SARS-CoV-2 using the Sansure Novel Coronavirus Nucleic Acid Diagnostic Kit.