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.

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