Comparing nasopharyngeal swab and early morning saliva for the identification of SARS-CoV-2

Abstract

Background

The ideal SARs-CoV-2 testing method would be accurate and also be patient-performed to reduce exposure to healthcare workers.  The aim of this study was to compare patient-performed testing based on a morning saliva sample with the current standard testing method, healthcare worker-collected sampling via a nasopharyngeal swab (NPS).

Methods

This was a prospective single center study which recruited 217 asymptomatic adult male participants in a COVID-19 quarantine center who had tested positive for SARS-CoV-2 8-10 days prior isolation. Paired NPS and saliva specimens were collected and processed within 5 hours of sample collection. Real time reverse transcriptase polymerase chain reaction (RT-PCR) targeting Envelope (E) and RNA-dependent RNA polymerase (RdRp) genes was performed and the results were compared.

Results

Overall, 160 of the 217 (74%) participants tested positive for Covid-19 based on saliva, NPS, or both testing methods. The detection rate for SARS-CoV-2 was higher in saliva compared to NPS testing (93.1%, 149/160 vs 52.5%, 84/160, p<0.001). The concordance between the two tests was 45.6% (virus was detected in both saliva and NPS in 73/160), while 47.5% were discordant (87/160 tested positive for one while negative for the other). The Ct values for E and RdRp genes were significantly lower in saliva specimens compared to NP swab specimens.

Conclusions

Our findings demonstrate that saliva is a better alternative specimen for detection of SARS-CoV-2. Taking into consideration, the simplicity of specimen collection, shortage of PPE and the transmissibility of the virus, saliva could enable self-collection for an accurate SARS-CoV-2 surveillance testing.