SCIENCE CHINA Life Sciences, Volume 63 , Issue 5 : 706-711(2020) https://doi.org/10.1007/s11427-020-1661-4

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

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  • ReceivedFeb 27, 2020
  • AcceptedMar 3, 2020
  • PublishedMar 4, 2020


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.

Funded by

the project of Jiangsu province medical youth talent(QNRC2016059)

Nanjing medical science and technique development foundation(ZKX17040,YKK18153)

the National Natural Science Foundation of China(81903382)

Cheung Kong Scholars Program of China.


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.

Interest statement

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



Figure S1 Date of asymptomatic COVID-19 infection onset among close contact in Nanjing and the distribution of travel history to Hubei.

Figure S2 Representative chest CT abnormalities of asymptomatic COVID-19 infections.

Figure S3 The abnormal blood test during hospitalization.

Figure S4 The calculation process of the communicable period.

Table S1 Clinical characteristics of 24 asymptomatic infections with COVID-19 grouped by cases with/without symptoms after diagnosis

Table S2 Clinical characteristics of 24 asymptomatic infections with COVID-19 grouped by grouped by cases with/without symptoms plus abnormal chest CT

The supporting information is available online at http://life.scichina.com and https://link.springer.com. The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.


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  • Figure 1

    The epidemiological and clinical characteristic of the 24 asymptomatic infections with COVID-19 screened among close contacts. The cases were successively listed according to the date of diagnosis. Date of diagnosis was defined as origin point, the contact history was reviewed; abnormal blood test and CT image upon admission were listed; and symptom and nucleic acid test were recorded during hospitalization.

  • Figure 2

    The transmission evidence from an asymptomatic COVID-19 carrier to his cohabited family members, and his wife admitted to the ICU after being infected.

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