BACKGROUND The coronavirus disease (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a major global public health issue . SARS-CoV-2 infection is confirmed by the detection of viral RNA using reverse transcription polymerase chain reaction (RT-PCR). Prolonged viral shedding has been reported in patients with SARS-CoV-2 infection, but the presence of viral RNA does not always correlate with infectivity . Therefore, the present study aimed to confirm the presence of viable virus in asymptomatic or mildly symptomatic patients in the later phase of the disease, more than two weeks after diagnosis .
METHOD Asymptomatic or mildly symptomatic COVID-19 patients who had been diagnosed with the disease at least two weeks previously and admitted to a community treatment center (CTC) from 15 March to 10 April 2020 were enrolled in this study . Nasopharyngeal and salivary swab specimens were collected from each patient . Using these specimens, RT-PCR assay and viral culture were performed . RESULT In total, 48 patients were enrolled in this study . There were no significant differences in baseline characteristics between the asymptomatic and mildly symptomatic patient groups . RT-PCR assay and viral culture of SARS-CoV-2 were performed using nasopharyngeal and salivary swabs . The results of RT-PCR performed using salivary swab specimens, in terms of cycle threshold (Ct) values, were similar to those of RT-PCR using nasopharyngeal swab specimens . In addition, no viable virus could be cultured from swab specimens collected from the late-phase COVID-19 patients with prolonged viral RNA shedding .
CONCLUSIONS In conclusion, our study suggests that even if viral shedding is sustained in asymptomatic or mildly symptomatic patients with later phase of COVID-19, it can be expected that the transmission risk of the virus is low . In addition, saliva can be used as a reliable specimen for the diagnosis of SARS-CoV-2 infection.