Viral kinetics of SARS-CoV-2 in asymptomatic carriers and presymptomatic patients

Abstract

From a total of 71 laboratory-confirmed cases, three presymptomatic patients and 10 patients with entirely asymptomatic infections were identified. In two of the three incubation period patients, the viral titer in the presymptomatic period was very high (Ct value<20). The median number of days to first negative RT-PCR in the asymptomatic carriers was 4.5 (range 2.5-9), and all asymptomatic carriers reached a first RT-PCR Ct>35 within 14 days after diagnosis. Patients who have COVID-19 may already be infectious before there are symptoms, and 14 days of isolation after diagnosis may be sufficient in entirely asymptomatic cases.

Keywords: Asymptomatic carrier; COVID-19; Isolation; Presymptomatic; Viral kinetics.

Figure 1

Viral load detected in nasal–throat swabs obtained from patients infected with SARS-CoV-2. The cycle threshold (Ct) values of the RNA-dependent RNA polymerase (RdRp) gene on reverse-transcriptase polymerase chain reaction (RT-PCR) assays of nasal–throat swabs obtained from (A) three incubation period patients with mild cases of COVID-19, and (B) 10 asymptomatic carriers. Ct = 35 is the cut-off for a positive result and Ct = 40 is a negative sample; Ct = 40 was the limit of detection.