J Korean Med Sci.  2020 Aug;35(31):e287. 10.3346/jkms.2020.35.e287.

Viral Load Kinetics of SARS-CoV-2Infection in Saliva in Korean Patients:a Prospective Multi-center Comparative Study

• Kim SE
• Lee JY
• Lee A
• Kim S
• Park KH
• Jung SI
• Kang SJ
• Oh TH
• Kim UJ
• Lee SY
• Kee SJ
• Jang HC

• KMID: 2505201
• DOI: http://doi.org/10.3346/jkms.2020.35.e287

Abstract

Background
This study was performed to compare the viral load and kinetics of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in saliva with those in standard nasopharyngeal/oropharyngeal (NP/OP) swabs.
Methods
Fifteen patients with SARS-CoV-2 infection from four hospitals were prospectively enrolled and matched samples of nasopharyngeal/oropharyngeal swabs and saliva were collected at Day 1 of admission and every other day till consequently negative for two times. Real-time reverse transcription polymerase chain reaction (rRT-PCR) was performed to detect the envelope (E) and RNA-dependent RNA polymerase (RdRP) genes.
Results
The cycle threshold values of saliva were comparable to those of NP/OP swabs overall (P = 0.720, Mann–Whitney U test). However, the overall sensitivity of rRT-PCR using saliva was 64% (34/53), which is lower than the 77% (41/53) using NP/OP swabs. The sensitivity of rRT-PCR using saliva was especially lower in early stage of symptom onset (1–5 days; 8/15; 53%) and in patients who did not have sputum (12/22; 55%).
Conclusion
Saliva sample itself is not appropriate for initial diagnosis of coronavirus disease 2019 (COVID-19) to replace NP/OP swabs, especially for the person who does not produce sputum. COVID-19 cannot be excluded when the test using saliva is negative, and it is necessary to retest using NP/OP swabs.

Keyword

SARS-CoV-2 PCR; Saliva; Nasopharyngeal Swab; Oropharyngeal Swab

Figure

• 

  Fig. 1 The Ct values of the RdRP gene. (A) In saliva and NP/OP swabs in 53 pairs of samples from 15 patients, excluding negative samples (Ct value > 35 for both). P = 0.720 by Mann-Whitney U-test. (B) In saliva, NP/OP swabs, and sputum in 93 samples from eight patients who had sputum, excluding negative samples (Ct value > 35 for all three). P = 0.664 by Kruskal–Wallis test. Lines are the mean ± standard error of the mean.Ct = cycle threshold, NP/OP = nasopharyngeal/oropharyngeal.

• 

  Fig. 2 The Ct values of the RdRP gene in saliva and NP/OP swabs in 53 pairs of samples from 15 patients according to the time periods from symptom onset. (A) Early stage (1–5 days after symptom onset). (B) Mid stage (6–10 days after symptom onset). (C) Late stage (≥ 11 days after symptom onset). Lines are the mean ± standard error of the mean. P = 0.267, 0.960 and 0.586 in each period respectively, by Mann-Whitney U test.Ct = cycle threshold, NP/OP = nasopharyngeal/oropharyngeal.

• 

  Fig. 3 Viral kinetics of each sample from (A) fifteen patients overall, (B) eight patients who had sputum, and (C) patients without sputum production. Expressed as the mean ± standard error of the mean. Slopes were calculated by simple linear regression. Slope were (A) −0.3754 (95% CI, −0.6924 to −0.0584) in NP/OP swabs, −0.1859 (95% CI, −0.5080 to 0.1362) in saliva; (B) −0.4330 (95% CI, −0.7922 to −0.0738) in saliva, −0.4958 (95% CI, −0.8746 to −0.1169) in NP/OP swabs, and −0.7950 (95% CI, −1.201 to −0.3894) in sputum (C) −0.4119 (95% CI, −1.157 to 0.3329) in NP/OP swabs, 0.1345 (95% CI, −0.6535 to 0.9225) in saliva.Ct = cycle threshold, NP/OP = nasopharyngeal/oropharyngeal.

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