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SARS-CoV-2 Ct values (A) and paired log-transformed antigen concentrations (B) measured in anterior nasal swab samples plotted by days since symptom onset for PCR-positive symptomatic adults (day 0 = the first day of symptoms). The blue bar in (A) outlines the window between Ct of 30 and Ct of 25. Abbreviations: Ct, Cycle threshold; PCR, polymerase chain reaction; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
