Risk factors associated with repositivity among COVID-19 patients
Table 3 presents the association between various potential risk factors and repositivity among COVID-19 patients before and after adjustment. A higher repositivity rate of males than females (23.4% [95% CI, 19.3 to 27.4] vs 18.1% [13.9 to 22.3]) was observed, but this difference was not statistically significant. The repositivity rate decreased with age, with 42.9% (27.9 to 57.8) for 0-17 years, 22.0% (18.1 to 25.9) for 18-44 years, 16.3% (10.7 to 21.9) for 45-59 years and 16.2% (9.1 to 23.2) for 60 or over years (P for trend = 0.0023), and decreased with severity, with 34.6% (27.2 to 42.0) for asymptomatic, 18.5% (10.1 to 27.0) for mild symptoms, 17.7% (14.3 to 21.2) for moderate symptoms and 10.8% (0.8 to 20.8) for severe symptoms (P for trend < 0.001). Manifestation of some symptoms at the first admission, such as fever (26.7% [22.1 to 31.4] vs 16.2% [12.6 to 19.8]), was associated with an increased risk of repositivity. In addition, comorbidities, CT lung abnormalities, and some clinical symptoms (such as fatigue, chills, and sore throat) were not separately assessed due to multicollinearity with age, severity and other clinical symptoms, and the repositivity rate of COVID-19 by these variables is shown in Table S1 .