Comparative evaluation of four SARS-CoV-2 antigen tests in hospitalized patients

Thommes, Lis; Burkert, Francesco Robert; Öttl, Karla-Wanda; Goldin, David; Loacker, Lorin; Lanser, Lukas; Griesmacher, Andrea; Theurl, Igor; Weiss, Günter; Bellmann-Weiler, Rosa

Objectives Rapid identification of infected subjects is a corner stone for control of a pandemic like the current one with the SARS-CoV-2. Easy to handle antigen tests can provide timely results which is of specific importance in a primary care setting. However, concerns exist regarding their sensitivity, which let us evaluate four commercially available tests in patients hospitalized for COVID-19. Methods We analyzed in parallel nasopharyngeal/oropharyngeal swabs from 87 consecutive patients admitted to our department with moderate to severe COVID-19 by means of quantitative RT-PCR (Cobas, Roche) and up to four antigen tests from different distributors. Antigen test results were linked to Ct (cycle threshold) values as a marker for infectivity of patients. Results We found that two out of four antigen tests correctly identified subjects with high viral loads (Ct ≤25) and three out of four tests detected more than 80% of subjects with a Ct ≤30 which is considered as a threshold for infectivity. However, one test investigated had a poor clinical performance. When investigating subjects with Ct values >30 we found that in up to 45% of the cases the antigen test was still positive. Conclusion Most antigen tests had a sufficient sensitivity to identify symptomatic subjects infected with SARS-CoV-2 and with transmissible infection. On the other hand, antigen testing may not be suitable to identify loss of infectivity in COVID-19 subjects during follow-up. Newly introduced antigen tests need to be validated in a clinical or primary care setting to define their clinical usefulness.