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.
Chan, J.F.W., Yuan, S., Kok, K.H., To, K.K.W., Chu, H., Yang, J., Xing, F., Liu, J., Yip, C.C.Y., Poon, R.W.S., et al. (2020). A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a study of a family cluster. Lancet 514–523.
Chang, D., Lin, M., Wei, L., Xie, L., Zhu, G., Dela Cruz, C.S., and Sharma, L. (2020). Epidemiologic and clinical characteristics of novel coronavirus infections involving 13 patients outside Wuhan, China. JAMA, doi: https://doi.org/10.1001/jama.2020.1623.
Chen, N., Zhou, M., Dong, X., Qu, J., Gong, F., Han, Y., Qiu, Y., Wang, J., Liu, Y., Wei, Y., et al. (2020). Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study. Lancet 507–513.
China, N.H.C.o.t.P.s.R.o. (2020). New coronavirus pneumonia prevention and control program (5th ed.) (in Chinese).
Ding, L., Cai, W., Jing J.Q., Zhang, X.X., Cai Y., Shi, J.W., Liang, Q.M., Zhang, L.F., Sun, L.Z., Qu, J.M., et al. (2020). An interim review of lessons from the novel coronavirus (SARS-CoV-2) outbreak in China. Sci Sin Vitae 50, doi: https://doi.org/10.1360/SSV-2020-0044.
Guan, W.J., Ni, Z.Y., Hu, Y., Liang, W.H., Ou, C.Q., He, J.X., Liu, L., Shan, H., Lei, C.L., Hui, D.S.C., et al. (2020). Clinical characteristics of coronavirus disease 2019 in China. N Engl J Med, doi 10.1056/NEJMoa2002032.
Heymann, D.L., and Shindo, N. (2020). COVID-19: what is next for public health? Lancet 542–545.
Huang, C., Wang, Y., Li, X., Ren, L., Zhao, J., Hu, Y., Zhang, L., Fan, G., Xu, J., Gu, X., et al. (2020). Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 395, 497–506.
Lu, R., Zhao, X., Li, J., Niu, P., Yang, B., Wu, H., Wang, W., Song, H., Huang, B., Zhu, N., et al. (2020). Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding. Lancet 395, 565–574.
Phan, L.T., Nguyen, T.V., Luong, Q.C., Nguyen, T.V., Nguyen, H.T., Le, H. Q., Nguyen, T.T., Cao, T.M., and Pham, Q.D. (2020). Importation and human-to-human transmission of a novel coronavirus in Vietnam. N Engl J Med 872–874.
Wikipedia. (2020). Diamond Princess (ship). https://en.wikipedia.org/wiki/Diamond_Princess_(ship)
Wu, J.T., Leung, K., and Leung, G.M. (2020). Nowcasting and forecasting the potential domestic and international spread of the 2019-nCoV outbreak originating in Wuhan, China: a modelling study. Lancet 395, 689–697.
Yang, Y., Lu, Q., Liu, M., Wang, Y., Zhang, A., Jalali, N., Dean, N., Longini, I., Halloran, M.E., Xu, B., et al. (2020). Epidemiological and clinical features of the 2019 novel coronavirus outbreak in China. medRxiv, doi: https://doi.org/10.1101/2020.02.10.20021675.
Zhang, Z., Li, X., Zhang, W., Shi, Z.L., Zheng, Z., and Wang, T. (2020). Clinical Features and Treatment of 2019-nCov Pneumonia Patients in Wuhan: Report of A Couple Cases. Virol Sin, doi: https://doi.org/10.1007/s12250-020-00203-8.
Zou, L., Ruan, F., Huang, M., Liang, L., Huang, H., Hong, Z., Yu, J., Kang, M., Song, Y., Xia, J., et al. (2020). SARS-CoV-2 viral load in upper respiratory specimens of infected patients. N Engl J Med NEJMc2001737.
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.
Electronic supplementary material
About this article
Cite this article
Hu, Z., Song, C., Xu, C. et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. Sci. China Life Sci. 63, 706–711 (2020). https://doi.org/10.1007/s11427-020-1661-4
- asymptomatic infections
- close contact