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. 2020 Mar 4;63(5):706–711. doi: 10.1007/s11427-020-1661-4

Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China

Zhiliang Hu 1,2,#, Ci Song 2,3,#, Chuanjun Xu 4,#, Guangfu Jin 2,3,#, Yaling Chen 1, Xin Xu 2, Hongxia Ma 2,3, Wei Chen 5, Yuan Lin 6, Yishan Zheng 7, Jianming Wang 2, Zhibin Hu 1,✉, Yongxiang Yi 1,✉, Hongbing Shen 2,3
PMCID: PMC7088568  PMID: 32146694

Abstract

Previous studies have showed clinical characteristics of patients with the 2019 novel coronavirus disease (COVID-19) and the evidence of person-to-person transmission. Limited data are available for asymptomatic infections. This study aims to present the clinical characteristics of 24 cases with asymptomatic infection screened from close contacts and to show the transmission potential of asymptomatic COVID-19 virus carriers. Epidemiological investigations were conducted among all close contacts of COVID-19 patients (or suspected patients) in Nanjing, Jiangsu Province, China, from Jan 28 to Feb 9, 2020, both in clinic and in community. Asymptomatic carriers were laboratory-confirmed positive for the COVID-19 virus by testing the nucleic acid of the pharyngeal swab samples. Their clinical records, laboratory assessments, and chest CT scans were reviewed. As a result, none of the 24 asymptomatic cases presented any obvious symptoms while nucleic acid screening. Five cases (20.8%) developed symptoms (fever, cough, fatigue, etc.) during hospitalization. Twelve (50.0%) cases showed typical CT images of ground-glass chest and 5 (20.8%) presented stripe shadowing in the lungs. The remaining 7 (29.2%) cases showed normal CT image and had no symptoms during hospitalization. These 7 cases were younger (median age: 14.0 years; P=0.012) than the rest. None of the 24 cases developed severe COVID-19 pneumonia or died. The median communicable period, defined as the interval from the first day of positive nucleic acid tests to the first day of continuous negative tests, was 9.5 days (up to 21 days among the 24 asymptomatic cases). Through epidemiological investigation, we observed a typical asymptomatic transmission to the cohabiting family members, which even caused severe COVID-19 pneumonia. Overall, the asymptomatic carriers identified from close contacts were prone to be mildly ill during hospitalization. However, the communicable period could be up to three weeks and the communicated patients could develop severe illness. These results highlighted the importance of close contact tracing and longitudinally surveillance via virus nucleic acid tests. Further isolation recommendation and continuous nucleic acid tests may also be recommended to the patients discharged.

Electronic Supplementary Material

Supplementary material is available for this article at 10.1007/s11427-020-1661-4 and is accessible for authorized users.

Keywords: COVID-19, asymptomatic infections, close contact, China

Electronic supplementary material

11427_2020_1661_MOESM1_ESM.pdf (466.2KB, pdf)

Supplementary material, approximately 467 KB.

Acknowledgements

The authors would like to thank the patients and the supporting staff in this study. This work was supported by the project of Jiangsu province medical youth talent (QNRC2016059), Nanjing medical science and technique development foundation (ZKX17040 and YKK18153), the National Natural Science Foundation of China (81903382), Cheung Kong Scholars Program of China.

Compliance and ethics The author(s) declare that they have no conflict of interest.

Footnotes

Contributed equally to this work

Contributor Information

Zhibin Hu, Email: zhibin_hu@njmu.edu.cn.

Yongxiang Yi, Email: ian0126@126.com.

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Supplementary Materials

11427_2020_1661_MOESM1_ESM.pdf (466.2KB, pdf)

Supplementary material, approximately 467 KB.

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