The gold-standard method for diagnosing COVID-19 is the polymerase chain reaction (PCR) test, which detects the coronavirus’s genetic material in a nose or throat swab. Now, a survey of more than 15,000 people has singled out the people most likely to receive false negatives on the test.
Caitlin Dugdale at Massachusetts General Hospital in Boston and her colleagues looked at PCR test results from about 15,000 people who showed COVID-19 symptoms or were thought for other reasons to be infected with SARS-CoV-2 (C. M. Dugdale
et al.
Open Forum Infect. Dis. Clinical, laboratory, and radiologic characteristics of patients with initial false-negative SARS-CoV-2 nucleic acid amplification test results; 2020). Nearly 2,700 individuals tested negative and had a second PCR test done within 2 weeks.
Among those who received a second test, 60 — or 2.2% — tested positive. Of these, 60% had their initial test either one day or less before symptom onset or more than 7 days after it, suggesting that the PCR test is most likely to yield a false negative in people tested early or late in the course of infection.