Effect of RNA quality to SARS-CoV-2 RT-qPCR detection from saliva

Saliva is an alternative sample material to nasopharyngeal swab in SARS- CoV- 2 diagnostics. We investigated possible aspects to improve the reliability of SARS- CoV- 2 detection from saliva. Saliva was collected from asymptomatic healthy subjects (n=133) and COVID- 19 patients (n=9). SARS- CoV- 2 detection was performed with quantitative reverse- transcriptase PCR (RT- qPCR) with two viral and one host target serving as an internal control. The use of internal control revealed that in the first RT- qPCR run 25???30 % of assays failed. The failure is associated with poor RNA quality. When the amount of RNA was cut down to half from the original amount, the performance of RT- qPCR was greatly enhanced (95 % of the assays succeeded). The quality of RNA was not affected by the use of different nucleic acid stabilizing buffers. Our study showed that saliva is suitable material for RT- qPCR based SARS- CoV- 2 diagnostics, but the use of internal control is essential to distinguish the true negative samples from failed assays.