Performance of antigenic detection of SARS-CoV-2 in nasopharyngeal samples

Lunca, C.; Cojocaru, C.; Gurzu, I. L.; Petrariu, F. D.; Cojocaru, E.

Objectives: SARS-CoV-2 virus detection on nasopharyngeal specimens to infected individuals has become a challenge for the COVID-19 pandemic outbreak. We aim at comparing the performance of antigenic detection of SARS-CoV-2 in nasopharyngeal samples via an immunochromatographic method to molecular detection via qRT-PCR. Materials and Methods: 47 nasopharyngeal exudates were collected from suspicious COVID-19 cases. The samples were performed both via the qualitative immuno-chromatographic method for S protein detection in the SARS-CoV-2 structure, using fluorescent labelled anti-protein S antibodies and via qRT-PCR test for the qualitative detection of the screening gene E and the specific ORF1ab region of the RNA-SARS-CoV-2. Results: There was a fair correlation between the positive antigen tests and the positive PCR assays measured through threshold cycle ORF1ab region (Ct orf). A better correlation was obtained between the antigen test results and the Ct orf when including patients with Ct orf below 25. Conclusions: Using antigen tests as screening tests is useful on symptomatic persons during the viral replication period, therefore during the contagious period. A positive test shows a high predictive value for infection, while a negative antigen test result via immuno-chromatography must be confirmed by a qRT-PCR test.