Covid-19 antigen testing: better than we know? A test accuracy study. Issue 9 (2nd September 2021)

• Record Type: Journal Article
• Authors: Homza, Miroslav; Zelena, Hana; Janosek, Jaroslav; Tomaskova, Hana; Jezo, Eduard; Kloudova, Alena; Mrazek, Jakub; Svagera, Zdenek; Prymula, Roman
• Is Part Of: Infectious diseases. Volume 53:Issue 9(2021)
• Page Start: 661
• Page End: 668
• Publication Date: 2021-09-02
• Subjects: Covid-19 -- SARS-CoV-2 -- antigen testing -- virus viability -- virus shedding -- sensitivity; Communicable diseases -- Periodicals; Communicable Diseases -- Periodicals; Communicable diseases; Periodicals; 616.9
• DOI: 10.1080/23744235.2021.1914857
• Languages: English
• ISSNs: 2374-4235

Abstract

Abstract: Background: Antigen testing for SARS-CoV-2 is considered to be less sensitive than the standard reference method – real-time PCR (RT-PCR). It has been suggested that many patients with positive RT-PCR 'missed' by antigen testing might be non-infectious. Methods: In a real-world high-throughput setting for asymptomatic or mildly symptomatic patients, 494 patients were tested using RT-PCR as well as a single lateral flow antigen test (Ecotest, AssureTech, China). Where the results differed, virus viability was evaluated by cell culture. The test parameters were calculated with RT-PCR and RT-PCR adjusted on viability as reference standards. Results: The overall sensitivity of the used antigen test related to the RT-PCR only was 76.2%, specificity was 97.3%. However, 36 out of 39 patients 'missed' by the antigen test contained no viable virus. After adjusting on that, the sensitivity grew to 97.7% and, more importantly for disease control purposes, the negative predictive value reached 99.2%. Conclusions: We propose that viability testing should be always performed when evaluating a new antigen test. A well-chosen and validated antigen test provides excellent results in identifying patients who are shedding viable virus (although some caveats still remain) in the real-world high-throughput setting of asymptomatic or mildly symptomatic individuals.