Sensitivity and Specificity of Two WHO Approved SARS-CoV2 Antigen Assays in Detecting Patients with SARS-CoV2 Infection

Background: SARS-CoV-2 rapid antigen (Ag) detection kits are widely used in addition to quantitative real-time PCR (RT-qPCR), as they are cheaper with a rapid turnaround time. As there are many concerns regarding their sensitivity and specificity, in different settings, we evaluated two WHO approved rapid Ag kits in a large cohort of Sri Lankan individuals. Methods: Paired nasopharangeal swabs were obtained from 4845 participants for validation of the SD-Biosensor rapid Ag assay and 3625 for the Abbott rapid Ag assay, in comparison to RT-qPCR. A short questionnaire was used to record symptoms at the time of testing, and blood samples were obtained from 2721 of them for detection of SARS-CoV-2 specific antibodies. Findings: The overall sensitivity of the SD-Biosensor Ag kit was 36.5% and the Abbott Ag test was 50.76%. The Abbott Ag test showed specificity of 99.4% and the SD-Biosensor Ag test 97.5%. At Ct values 30 (46.1 to 82.9%). 32.1% of those who gave a positive result with the SD-Biosensor Ag test and 26.3% of those who gave positive results with the Abbott Ag test had SARS-CoV-2 antibodies at the time of detection. Interpretation: Both rapid Ag tests appeared to be highly sensitive in detecting individuals at lower Ct values, in a community setting in Sri Lanka, but it will be important to further establish the relationship to infectivity. Funding Statement: We are grateful to the World Health Organization, UK Medical Research Council and the Foreign and Commonwealth Office. Declaration of Interests: No conflicts of interests. Ethics Approval Statement: Ethics approval was obtained from the Ethics Review Committee of the University of Sri Jayewardenepura.