Prospective Study Tracks Peak SARS-CoV-2 Detection Performance for Rapid Antigen Tests

Researchers reporting in the Annals of Internal Medicine used a prospective cohort study approach to track rapid antigen test (Ag-RDT) performance over time in asymptomatic or symptomatic individuals infected with SARS-CoV-2. The team, which includes investigators at the University of Massachusetts Chan Medical School, the US Food and Drug Administration, and elsewhere started with more than 7,300 participants, focusing on 5,353 symptom-free individuals who tested negative for SARS-CoV-2 when the study began. With RT-PCR and Ag-RDTs done over time, the authors identified 154 SARS-CoV-2-positive individuals, including 57 individuals with symptoms and 97 asymptomatic cases. In a setting where Ag-RDTs were given once, twice, or three times in 48-hour intervals, their results suggest that optimal Ag-RDT performance was achieved with two tests taken 48 hours apart in symptomatic individuals or three tests done at 48-hour intervals in individuals without symptoms. "The public health implications of our findings are that people testing for SARS-CoV-2 should exercise caution despite an initial negative result on an Ag-RDT and favor mask wearing and avoiding crowded places if they suspect they may be infected or have been exposed," the authors write. In contrast, they note that "rates of false-positive results in the study were low; therefore, any Ag-RDT-positive result should be considered positive without the need to retest."