Accuracy of anterior nasal swab rapid antigen tests compared with RT-PCR for massive SARS-CoV-2 screening in low prevalence population.

Background The aim was to determine the accuracy of anterior nasal swab in rapid antigen (Ag)-tests in a low SARS-CoV-2 prevalence and massive screened community. Methods Individuals, aged 18 years or older, who self-booked an appointment for real-time reverse transcriptase-polymerase chain reaction (RT-PCR)-test in March 2021 at a public test center in Copenhagen, Denmark were included. An oropharyngeal swab was collected for RT-PCR-testing, followed by a swab from the anterior parts of the nose examined by Ag-test (SD Biosensor). Accuracy of the Ag-test was calculated with RT-PCR as reference. Results We included 7,074 paired conclusive tests (n= 3461, female: 50.7%). The median age was 48 years (IQR: 36-57 years). The prevalence was 0.9% i.e. 66 tests were positive on RT-PCR. 32 had a paired positive Ag-test. The sensitivity was 48.5% and the specificity was 100%. Conclusion This study conducted in a low prevalence setting in a massive screening set-up showed that the Ag-test had a sensitivity of 48.5% and a specificity of 100% i.e. no false positive tests. The lower sensitivity is a challenge especially if Ag testing is not repeated frequently allowing this scalable test to be a robust supplement to RT-PCR testing in an ambitious public SARS-CoV-2 screening.