Patterns of viral clearance in the natural course of asymptomatic COVID-19: Comparison with symptomatic non-severe COVID-19

•Approximately 17% of the patients with COVID-19 exhibited no symptoms.•The median time from diagnosis to negative conversion was about 2 weeks in the natural course of asymptomatic COVID-19.•Time until negative conversion was shorter in asymptomatic COVID-19 than in symptomatic COVID-19.•Rebound of cycle threshold values was not uncommon in follow-up RT-PCR assays. The aim of this study was to elucidate patterns of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) clearance in the natural course of asymptomatic coronavirus disease 2019 (COVID-19). Consecutive patients with non-severe COVID-19 were included retrospectively. Asymptomatic patients with a normal body temperature and no evidence of pneumonia throughout the disease course were assigned to the asymptomatic group. The reverse transcription PCR (RT-PCR) assay was repeated every two to five days after the first follow-up RT-PCR assay. Negative conversion was defined as two consecutive negative RT-PCR assay results within a 24-h interval. Rebound of the cycle threshold (Ct) value was defined as negative from the single RT-PCR assay and positive from the following assay. Among a total of 396 patients identified (median age 42.5 years (interquartile range (IQR) 25.0–55.0 years), 35.6% male), 68 (17.2%) were assigned to the asymptomatic group and 328 (82.8%) to the symptomatic group. The time until negative conversion was significantly shorter in the asymptomatic group than in the symptomatic group: median 14.5 days (IQR 11.0–21.0 days) and 18.0 days (IQR 15.0–22.0 days), respectively (p = 0.001). Rebound of Ct values was observed in 78 patients (19.7%). Time until negative conversion is shorter in asymptomatic COVID-19 than in symptomatic COVID-19. Rebound of Ct values is not uncommon.