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. 2021 May 4;72(9):e352-e356.
doi: 10.1093/cid/ciaa1156.

Comparing Nasopharyngeal Swab and Early Morning Saliva for the Identification of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Mohan Rao  1 , Fairuz A Rashid  1 , Fashihah S A H Sabri  1 , Nur Nadia Jamil  1 , Rozainanee Zain  1 , Rohaidah Hashim  1 , Fairuz Amran  1 , Huey Tean Kok  2 , Md Anuar Abd Samad  2 , Norazah Ahmad  1
Affiliations

Comparing Nasopharyngeal Swab and Early Morning Saliva for the Identification of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Mohan Rao et al. Clin Infect Dis. .

Abstract

Background: The ideal severe acute respiratory syndrome coronavirus 2 (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 coronavirus disease 2019 (COVID-19) quarantine center who had tested positive for SARS-CoV-2 8-10 days prior to isolation. Paired NPS and saliva specimens were collected and processed within 5 hours of sample collection. Real time reverse transcription 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 < .001). The concordance between the 2 tests was 45.6% (virus was detected in both saliva and NPS in 73/160), whereas 47.5% were discordant (87/160 tested positive for 1 whereas negative for the other). The cycle threshold (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.

Keywords: COVID-19; SARS-CoV-2; nasopharyngeal swab; pandemic; saliva.

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Figures

Figure 1.
Figure 1.
Boxplots of SARS-CoV-2 Ct value (mean and interquartile range) of both E-gene and RdRp-gene of all the positive specimens. Ct values of both genes were lower in the saliva than nasopharyngeal swabs of studied asymptomatic individuals. Also included are Ct values of internal control (Human RnaseP-gene) of all the samples in both specimens. Abbreviations: Ct, cycle threshold; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
Figure 2.
Figure 2.
Histogram represents distribution of Ct value of concordant (matched) specimens (n = 73) compared between specimen types and the targeted genes. Saliva has large distribution of Ct value of all the targeted genes in comparison to NPS. Meanwhile, nasopharyngeal swab shares most density of the histogram edging the upper limit. Abbreviation: Ct, cycle threshold.
See this image and copyright information in PMC

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