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. 2022 Mar 14;12(3):710.
doi: 10.3390/diagnostics12030710.

Evaluation of the Diagnostic Accuracy of Nasal Cavity and Nasopharyngeal Swab Specimens for SARS-CoV-2 Detection via Rapid Antigen Test According to Specimen Collection Timing and Viral Load

Seungjun Lee  1 , Kristin Widyasari  1 , Hye-Ryun Yang  2 , Jieun Jang  2 , Taejoon Kang  3 , Sunjoo Kim  1   2   4
Affiliations

Evaluation of the Diagnostic Accuracy of Nasal Cavity and Nasopharyngeal Swab Specimens for SARS-CoV-2 Detection via Rapid Antigen Test According to Specimen Collection Timing and Viral Load

Seungjun Lee et al. Diagnostics (Basel). .

Abstract

The rapid diagnosis of SARS-CoV-2 is an essential aspect in the detection and control of the spread of COVID-19. We evaluated the accuracy of the rapid antigen test (RAT) using samples from the nasal cavity and nasopharynx based on sample collection timing and viral load. We enrolled 175 patients, of which 71 patients and 104 patients had tested positive and negative, respectively, based on real time-PCR. Nasal cavity and nasopharyngeal swab samples were tested using STANDARD Q COVID-19 Ag tests (Q Ag, SD Biosensor, Korea). The sensitivity of the Q Ag test was 77.5% (95% confidence interval [CI], 67.8−87.2%) for the nasal cavity and 81.7% (95% [CI, 72.7−90.7%) for the nasopharyngeal specimens. The RAT results showed a substantial agreement between the nasal cavity and nasopharyngeal specimens (Cohen’s kappa index = 0.78). The sensitivity of the RAT for nasal cavity specimens exceeded 89% for <5 days after symptom onset (DSO) and 86% for Ct of E and RdRp < 25. The Q Ag test performed fairly well, especially in the early DSO when a high viral load was present, and the nasal cavity swab can be considered an alternative site for the rapid diagnosis of COVID-19.

Keywords: COVID-19 testing; SARS-CoV-2; detection; nasal cavity; rapid antigen test.

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Conflict of interest statement

No potential conflict of interest was reported by the authors.

Figures

Figure 1
Figure 1
Color intensity scale of the STANDARD Q COVID-19 Ag test (Q Ag) (SD Biosensor, Suwon, Korea). The color intensities that appeared on the test kits were compared with the color scale and were recorded within the range of 0 to 21 as negative to very strong, respectively.
Figure 2
Figure 2
Spearman’s correlation analysis of the color intensity of the rapid antigen test (0: negative; 1: very weak; 21: very strong) and Ct values for the E determined by real-time PCR. (a) nasopharyngeal swab specimens (rho = −0.876, p < 0.01), (b) nasal cavity swab specimens (rho = −0.725, p < 0.01).
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