Comparing Nasopharyngeal Swab and Early Morning Saliva for the Identification of Severe Acute Respiratory Syndrome Coronavirus 2 (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.

Validation of self-collected buccal swab and saliva as a diagnostic tool for COVID-19

“…It is also reported to have a reduced time and cost [12], and decreased risk of transmission in the community and to HCWs, making it a convenient and safe means of mass testing. There is increasing evidence that the viral load in saliva is comparable or higher than that in the nasopharynx [4,[13][14][15]. We have shown that the CT values were comparable between saliva and NPS, representing a similar viral load in both samples.…”

“…However, the low PPA of 66.7% may limit its suitability to replace NPS as the gold standard diagnostic test. Existing studies have also shown varying PPA or concordance rates, when comparing saliva detection rates to NPS, with reported positive concordance rates ranging from 45.6% [13] to 94.8% [17]. The vast differences in concordance rates may be accounted for by the limitations in sample collection.…”

Performance of at-home self-collected saliva and nasal-oropharyngeal swabs in the surveillance of COVID-19

“…Next, we compared the Ct values between the groups G3 (NOP+/saliva-) and G4 (NOP+/saliva+). It was observed that the Ct values were lower in patients positive in both NOP and saliva samples (median [IQR], 21.5 [19][20][21][22][23][24][25][26][27]) compared to those positive only in NOP samples (29 [25][26][27][28][29][30][31][32][33], P = 0.01, Wilcoxon's rank-sum test) for the E gene. Moreover, these results were also found for the S gene (Figure 2(b)).…”

Pooled Saliva Specimens for SARS-CoV-2 Testing

“…When this study began, saliva was not an accepted specimen type, and procurement of saliva collection devices with stabilizers was limiting. (Table S1) (2)(3)(4)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)). Importantly, the tested population, the saliva collection method, and the processing protocol have varied between the studies, making comparison of results challenging.…”