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Viral RNA level, serum antibody responses, and transmission risk in discharged COVID-19 patients with recurrent positive SARS-CoV-2 RNA test results: a population-based observational cohort study

By Chao Yang, Min Jiang, Xiaohui Wang, Xiujuan Tang, Shisong Fang, Hao Li, Le Zuo, Yixiang Jiang, Yifan Zhong, Qiongcheng Chen, Chenli Zheng, Lei Wang, Shuang Wu, Weihua Wu, Hui Liu, Jing Yuan, Xuejiao Liao, Zhen Zhang, Yiman Lin, Yijie Geng, Huan Zhang, Huanying Zheng, Min Wan, Linying Lu, Xiaohu Ren, Yujun Cui, Xuan Zou, Tiejian Feng, Junjie Xia, Ruifu Yang, Yingxia Liu, Shujiang Mei, Baisheng Li, Zhengrong Yang, Qinghua Hu

Posted 26 Jul 2020
medRxiv DOI: 10.1101/2020.07.21.20125138

Background Managing discharged COVID-19 (DC) patients with recurrent positive (RP) SARS-CoV-2 RNA test results is challenging. We aimed to comprehensively characterize the viral RNA level and serum antibody responses in RP-DC patients and evaluate their viral transmission risk. Methods A population-based observational cohort study was performed on 479 DC patients discharged from February 1 to May 5, 2020 in Shenzhen, China. We conducted RT-qPCR, antibody assays, neutralisation assays, virus isolation, whole genome sequencing (WGS), and epidemiological investigation of close contacts. Findings Of 479 DC patients, the 93 (19%) RP individuals, including 36 with multiple RP results, were characterised by young age (median age: 34 years, 95% confidence interval [CI]: 29-38 years). The median discharge-to-RP length was 8 days (95% CI: 7-14 days; maximum: 90 days). After readmission, RP-DC patients exhibited mild (28%) or absent (72%) symptoms, with no disease progression. The viral RNA level in RP-DC patients ranged from 1.9-5.7 log10 copies/mL (median: 3.2, 95% CI: 3.1-3.5). At RP detection, the IgM, IgG, IgA, total antibody, and neutralising antibody (NAb) seropositivity rates in RP-DC patients were 38% (18/48), 98% (47/48), 63% (30/48), 100% (48/48), and 91% (39/43), respectively. Regarding antibody levels, there was no significant difference between RP-DC and non-RP-DC patients. The antibody level remained constant in RP-DC patients pre- and post-RP detection. Virus isolation of nine representative specimens returned negative results. WGS of six specimens yielded only genomic fragments. No clinical symptoms were exhibited by 96 close contacts of 23 RP-DC patients; their viral RNA (96/96) and antibody (20/20) test results were negative. After full recovery, 60% of patients (n=162, 78 no longer RP RP-DC and 84 non-RP-DC) had NAb titres of [≥]1:32. Interpretation RP may occur in DC patients following intermittent and non-stable excretion of low viral RNA levels. RP-DC patients pose a low risk of transmitting SARS-CoV-2. An NAb titre of [≥]1:32 may provide a reference indicator for evaluating humoral responses in COVID-19 vaccine clinical trials.

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