The lack of an established reference standard, use of differing sample collection and preparation methods, and an incomplete understanding of viral dynamics across the time course of infection hamper rigorous assessment of the diagnostic accuracy of the many newly introduced SARS–CoV-2 assays (36). Serum and urine are usually negative for the presence of viral nucleic acid, regardless of illness severity (33). Of importance, the ability of RT-PCR assays to rule out COVID-19 on the basis of upper respiratory tract samples obtained at a single time point remains unclear. Conversely, after a patient has had a positive test result, several authorities have recommended obtaining at least 2 negative upper respiratory tract samples, collected at intervals of 24 hours or longer, to document SARS–CoV-2 clearance (37, 38).