Evaluating the use of posterior oropharyngeal saliva in a point-of-care assay for the detection of SARS-CoV-2

Jonathan Hon-Kwan Chen, Cyril Chik-Yan Yip, Rosana Wing-Shan Poon, Kwok-Hung Chan, Vincent Chi-Chung Cheng, Ivan Fan-Ngai Hung, Jasper Fuk-Woo Chan, Kwok-Yung Yuen, Kelvin Kai-Wang To, Jonathan Hon-Kwan Chen, Cyril Chik-Yan Yip, Rosana Wing-Shan Poon, Kwok-Hung Chan, Vincent Chi-Chung Cheng, Ivan Fan-Ngai Hung, Jasper Fuk-Woo Chan, Kwok-Yung Yuen, Kelvin Kai-Wang To

Abstract

During the Coronavirus disease 2019 (COVID-19) pandemic, logistic problems associated with specimen collection limited the SARS-CoV-2 testing, especially in the community. In this study, we assessed the use of posterior oropharyngeal saliva as specimens for the detection of SARS-CoV-2 in an automated point-of-care molecular assay. Archived nasopharyngeal swab (NPS) and posterior oropharyngeal saliva specimens of 58 COVID-19 patients were tested with the Xpert® Xpress SARS-CoV-2 assay. SARS-CoV-2 was detected in either NPS or saliva specimens of all patients. Among them, 84.5% (49/58) tested positive in both NPS and saliva, 10.3% (6/58) tested positive in NPS only, and 5.2% (3/58) tested positive in saliva only. No significant difference in the detection rate was observed between NPS and saliva (McNemar's test p = 0.5078). The detection rate was slightly higher for N2 (NPS 94.8% and Saliva 93.1%) than that of the E gene target (Saliva: 89.7% vs 82.8%) on both specimen types. Significantly earlier median Ct value was observed for NPS comparing to that of saliva on both E (26.8 vs 29.7, p = 0.0002) and N2 gene target (29.3 vs 32.3, p = 0.0002). The median Ct value of E gene target was significantly earlier than that of the N2 gene target for both NPS (26.8 vs 29.3, p < 0.0001) and saliva (29.7 vs 32.3, p < 0.0001). In conclusion, posterior oropharyngeal saliva and NPS were found to have similar detection rates in the point-of-care test for SARS-CoV-2 detection. Since posterior oropharyngeal saliva can be collected easily, the use of saliva as an alternative specimen type for SARS-CoV-2 detection is recommended.

Keywords: COVID-19; SARS-CoV-2; nasopharyngeal swab; point-of-care testing; saliva.

Conflict of interest statement

No potential conflict of interest was reported by the author(s).

Figures

Figure 1.
Figure 1.
Comparison of Ct values. (A) and (B) Comparison of Ct values between NPS and saliva specimens for (A) E and (B) N2. (C) and (D) Comparison of Ct values between E and N2 for (C) NPS and (D) saliva.
Figure 1.
Figure 1.
Comparison of Ct values. (A) and (B) Comparison of Ct values between NPS and saliva specimens for (A) E and (B) N2. (C) and (D) Comparison of Ct values between E and N2 for (C) NPS and (D) saliva.

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Source: PubMed

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