Clinical Characteristics, Risk Factor and Transmission of the COVID-19 Discharged Cases with Positive Retest in Guangzhou, China: A Retrospective Cohort Study

Background: Some cases retested positive for SARS-CoV-2 following negative testing results and discharge, which attracted widespread concern. However, the potential risk factors associated with re-detectable positive tests in a large sample of cases who recovered from COVID-19 has not been well estimated. Methods: A total of 745 discharged COVID-19 cases were enrolled between 30 January and 9 September 2020 in Guangzhou, China. Data on the clinical characteristics, comorbidities, drug therapy, RT-PCR testing, and contact modes to close contacts were collected. Re-positive cases were confirmed by guidelines issued by China. The re-positive rate of in different settings was calculated. Univariable and multivariable logistic regression models were used to explore the potential risk factors associated with COVID-19 re-positivity. Findings: Among 745 discharged cases, 157 (21.1%; 95%CI, 18.2% to 24.0%) were retested positive with 55 (35.0%) of asymptomatic, 15 (9.6%) of mild, 83 (52.9%) of moderate and 4 (2.6%) of severe at the first admission. The median time from discharge to re-positivity was 8.0 days (IQR, 8.0 to 14.0 days). Most re-positive cases were without clinical symptoms and lymphocyte cell counts increased than before. The likelihood of re-positive testing for SARS-CoV-2 RNA was significantly higher among cases with younger age (OR, 3.88; 95%CI, 1.74 to 8.66, 0 to 17 years old), asymptomatic severity (OR, 4.36; 95%CI, 1.47 to 12.95) and without clinical symptoms (OR, 1.89; 95%CI, 1.32 to 2.70, without fever). Interpretation: We found that the re-positive rate of COVID-19 was relatively high, and they were re-tested positive with median days 8.0 to 14.0 post-discharge. Re-positive results were mainly observed in young cases without severe clinical symptoms. These findings suggest that a significant proportion of cases could carry virus fragments for a long time, and effective management, such as prolonged quarantine phase of discharged cases, is necessary. Funding Statement: The Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme; the Construction of High-level University of Guangdong; Young Elite Scientists Sponsorship Program by CAST; the National Natural Science Foundation of China; the Zhejiang University special scientific research fund for COVID-19 prevention and control. Declaration of Interests: We declare no competing interests. Ethics Approval Statement: This study was reviewed and approved by the Ethics Committee of GZCDC. As required by the National Health Commission of China, CDCs were responsible for the work for an ongoing public health response to COVID-19, and our cohort study was based on the data by GZCDC. Patients were informed about the surveillance before providing written consent, and data were collected and anonymized for analysis. All analysis of personally identifiable data took place onsite at the GZCDC.