Clinical characteristics of 745 patients with COVID-19
A total of 745 patients who officially recovered from COVID-19 were enrolled in this study, and they were all tested for SARS-CoV-2 by RT-PCR after discharge. Up to September 21, 2020, 157 patients (21.1%; 95% CI, 18.2 to 24.0) retested positive by RT-PCR and were transferred to the designated hospital. Fig. S1 shows the distribution of COVID-19 patients by date of the first admission, and the characteristics at the first admission of the 157 positive retest patients are shown in Table 1 . Positive retest results were observed in patients in all age groups (age ranging from 3 months to 82.0 years, with a median age of 33.0 years), which was significantly younger than that of negative retest patients (median age of 38.0 years). The days from the first admission to discharge of positive retest patients were significantly shorter than those of negative retest patients (11.2 [5.5, 16.4] vs. 13.0 [8.0, 20.0] days). During their first admission, all patients were updated by the progression of their illness, and the most severe condition was their final severity designation. One in three positive retest patients was asymptomatic compared with one in six negative retest patients (P <0.001). The positive retest patients had fewer comorbidities (such as cardiovascular disease, 1 [0.6%] vs. 29 [4.9%]), were less likely to be treated with anti-infective drugs (58 [36.9%] vs. 308 [52.4%]) and were likely to be in the ICU (4 [2.6%] vs. 37 [6.3%]). After discharge from the hospital, RT-PCR testing was performed regularly, and the median number of tests was 4.0 times (IQR, 3.0 to 6.0 times) for positive retest patients, which was significantly greater than that of negative retest patients (P <0.001). The median time for discharged patients retested as being viral RNA-positive was 8.0 days (IQR, 8.0 to 14.0 days) after discharge (Table 1 and Fig. 2 ). After discharge, 4 (2.6%) patients had symptoms of dry cough, 10 (6.4%) patients had expectoration, 2 (1.3%) patients had sore throat and 2 (1.3%) had fatigue, which was lower than that of the first admission. Among the 127 patients who underwent CT examination, 104 (81.3%) patients had abnormal but obvious absorption. Lymphocyte cell counts and lymphocyte cell percentages were increased compared with those before (Table 2 ).