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Viral culture results and contact tracing data confirm that antigen tests may fail to catch 20% of symptomatic and >80% of asymptomatic COVID-19 cases.
Lateral flow antigen tests (LFATs), also known as rapid antigen tests, use a device with an absorbent pad at one end and a reading window at the other to detect SARS-CoV-2 antigen in nasal swab samples. They have become preferred worldwide for detecting SARS-CoV-2 infections because of their low cost and rapidly available results, despite limited sensitivity. Nonetheless, the likelihood of infectious COVID-19 cases being missed by false-negative LFAT results has not been closely evaluated. U.K. researchers reanalyzed and linked the data from four studies of LFAT accuracy in relation to viral load as indicated by RT-PCR assays, viral culture, and contact tracing. Settings included a test-and-trace center (70 symptomatic individuals), mass testing (111 asymptomatic individuals), and a university screen (62 asymptomatic students).
The Innova LFAT (primarily used in the U.K.) would miss a predicted 20% of symptomatic cases at the test-and-trace center who had positive viral cultures, 29% of asymptomatic individuals in mass testing, and 81% of students. Of the sources of secondary cases, 38%, 47%, and 90% would be missed, respectively. Further modeling suggested that to attain 97% sensitivity for probable infectious cases, LFATs should be able to detect viral loads 1000–10,000 times lower than the current limit of detection — unachievable with the currently available technology.
Créditos: Comité científico Covid