Background: The clinical course and viral detection period in mild or asymptomatic coronavirus disease 2019 (COVID-19) patients are not yet known. The presumed low diagnostic sensitivity of upper respiratory specimens for Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) makes it difficult to confirm infection and recommend de-isolation.
Methods: We retrospectively reviewed real-time reverse transcriptase-polymerase chain reaction (RT-PCR) test results of mild or asymptomatic COVID-19 patients who were admitted at the Daegu-Gyeongbuk 7th community treatment centre in Korea between 9 March 2020 and 10 April 2020. Patients underwent an upper respiratory RT-PCR test every week until discharge. From the RT-PCR results, we evaluated the rate of prolonged (>3 weeks) SARS-CoV-2 RNA positivity. We analysed the proportion of reversed results, defined as a positive or indeterminate result one day after a negative RT-PCR result, according to time (<14, 15-21, 22-28, >28 days) from the initial positive RT-PCR result.
Results: In 23% (69/300) of patients, SARS-CoV-2 was detected more than 3 weeks after the initial positive RT-PCR. In 14% (42/300) of patients, the RT-PCR results were positive for more than 4 weeks. For 37.5% (152/405) of negative RT-PCR results, the results were reversed in the next day's test. And 43.5% (123/283) of negative RT-PCR results were reversed within 3 weeks of diagnosis.
Conclusions: The detection of SARS-CoV-2 lasting more than 3 weeks was common in mild or asymptomatic patients. Upper respiratory RT-PCR results were frequently reversed from negative to positive.