Accuracy of rapid antigen testing for COVID-19 in shelter settings

BackgroundThe COVID-19 pandemic disproportionally affected congregate living settings, including shelters. COVID-19 transmission can have more adverse outcomes in these settings due to the vulnerability of residents. Point of care rapid antigen testing (RAT) represents a strategy with potential benefits for COVID-19 detection in shelters, including rapid results, ease of use, cost-effectiveness, and early detection. ObjectivesOur primary objective was to assess the real-world test accuracy of RAT for COVID-19 using the Quidel Sofia 2 Flu + SARS Antigen fluorescent immunoassay (Sofia RAT) compared to polymerase chain reaction (PCR) testing among shelter residents in Ontario, Canada. Study DesignA consecutive sample of 102 residents across six shelters who were symptomatic for, or exposed to COVID-19 were included. The RAT and PCR samples were taken on the same day for each participant. Results from the Sofia RAT were compared to PCR test results to determine test accuracy. Participant demographic data could not be collected due to workforce constraints. ResultsWe reported our methods and findings using the QUality Assessment tool of Diagnostic Accuracy Studies (QUADAS-2) guidelines. Sofia 2 RAT specificity was 97.9% (95% CI: 92.7% to 99.7%) for COVID-19 compared to PCR. Due to a lack of true positive cases, sensitivity could not accurately be calculated (0.00% (95% CI: 0.00% to 52.2%)). ConclusionThese data suggest that the Sofia RAT is a highly specific test for COVID-19.