Performance of six rapid diagnostic tests for SARS-CoV-2 antigen detection and implications for practical use

BACKGROUND: Direct detection of SARS-CoV-2 viral proteins in nasopharyngeal swabs using lateral flow immunoassays is a simple, fast and cheap approach to diagnose the infection. AIMS AND METHODS: The performance of 6 SARS-CoV-2 antigen rapid diagnostic tests has been assessed in 634 hospitalized patients or outpatients including 297 patients found to be positive for SARS-CoV-2 RNA by means of RT-PCR and 337 patients presumed to be SARS-CoV-2 RNA-negative. RESULTS: The specificity of SARS-CoV-2 RDTs was generally high (398.5%). One assay had a lower specificity of 93.2%. The overall sensitivity of the 6 RDTs was variable, from 32.3% to 61.7%. Sensitivity correlated with the delay of sampling after the onset of symptoms and the viral load estimated by the Ct value in RT-PCR. Four out of 6 RDTs tested achieved sensitivities 380% when clinical specimens were collected during the first 3 days following symptom onset or with a Ct value ≤25. CONCLUSIONS: The present study shows that SARS-CoV-2 antigen can be easily and reliably detected by RDTs. These tests are easy and rapid to perform. However, the specificity and sensitivity of COVID-19 antigen RDTs may widely vary across different tests and must therefore be carefully evaluated before releasing these assays for realworld applications.