Antigen testing for SARS-CoV-2 (AGT) is generally considered inferior to RT-PCR testing in terms of sensitivity. However, little is known about the infectiousness of RT-PCR positive patients who pass undetected by AGT. In a screening setting for mildly symptomatic or asymptomatic patients with high COVID-19 prevalence (30-40%), 1141 patients were tested using one of five AGTs and RT-PCR. Where the results differed, virus viability in the samples was tested on cell culture (CV-1 cells). The test battery included AGTs by JOYSBIO, Assure Tech, SD Biosensor, VivaChek Biotech and NDFOS. Sensitivities of the ATGs compared to RT-PCR ranged from 42% to 76%. The best test yielded a 76% sensitivity, 97% specificity, 92% positive, and 89% negative predictive values, respectively. However, in the best performing ATG tests, almost 90% of samples with "false negative" AGT results contained no viable virus. Corrected on the virus viability, sensitivities grew to 81-97% and, with one exception, the tests yielded high specificities >96%. Performance characteristics of the best test after adjustment were 96% sensitivity, 97% specificity, 92% positive, and 99% negative predictive values (high prevalence population). We, therefore, believe that virus viability should be considered when assessing the AGT performance. Also, our results indicate that a well-performing antigen test could in a high-prevalence setting serve as an excellent tool for identifying patients shedding viable virus. We also propose that the high proportion of RT-PCR-positive samples containing no viable virus in the group of "false negatives" of the antigen test should be further investigated with the aim of possibly preventing needless isolation of such patients.

Department of Biomedical Sciences Faculty of Medicine University of Ostrava Syllabova 19 703 00 Ostrava Czech Republic

Department of Clinical Biochemistry Institute of Laboratory Medicine University Hospital Ostrava 17 Listopadu 1790 5 708 00 Ostrava Czech Republic

Department of Epidemiology and Public Health Faculty of Medicine University of Ostrava Syllabova 19 703 00 Ostrava Czech Republic

Department of Internal Medicine Faculty of Medicine University of Ostrava Syllabova 19 703 00 Ostrava Czech Republic

Faculty of Medicine Hradec Kralove Charles University Prague Simkova 870 500 03 Hradec Kralove Czech Republic

Faculty of Medicine University of Ostrava Syllabova 19 703 00 Ostrava Czech Republic

Hospital Karvina Raj Vydmuchov 399 734 01 Karvina Czech Republic

Institute of Public Health Ostrava Partyzánské Náměstí 7 702 00 Ostrava Czech Republic

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