Int J Med Sci 2020; 17(14):2187-2193. doi:10.7150/ijms.47576

Research Paper

Determination of risk factors for predicting the onset of symptoms in asymptomatic COVID-19 infected patients

Pei-Yao Tao1*, Ling Leng2*, Kun Liu3, Ri-Hua Zhou4, Yue-Chun Hu5, Shang-Jie Wu6, Yu-Dong Xiao1✉, Jun Liu1✉

1. Department of Radiology, The Second Xiangya Hospital, Central South University, Changsha, China, 410011.
2. Department of Cell Biology, School of Basic Medical Science, Tianjin Medical University, Tianjing, China, 300070.
3. Department of Infection and rehabilitation, Yiyang The Fourth People's Hospital, Yiyang, China, 413000.
4. Medical Department, Chenzhou The Second People's Hospital, Chenzhou, China, 423000.
5. Department of Radiology, Loudi Central Hospital, Nanhua University, Loudi, China, 417000.
6. Department of Pulmonary and Critical Care Medicine, The Second Xiangya Hospital, Central South University, Changsha, China, 410011.
*These authors contributed equally to this study.

This is an open access article distributed under the terms of the Creative Commons Attribution License ( See for full terms and conditions.
Tao PY, Leng L, Liu K, Zhou RH, Hu YC, Wu SJ, Xiao YD, Liu J. Determination of risk factors for predicting the onset of symptoms in asymptomatic COVID-19 infected patients. Int J Med Sci 2020; 17(14):2187-2193. doi:10.7150/ijms.47576. Available from

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Background: The number of asymptomatic infected patients with coronavirus disease 2019 (COVID-2019) is rampaging around the world but limited information aimed on risk factors of asymptomatic infections. The purpose of this study is to investigate the risk factors of symptoms onset and clinical features in asymptomatic COVID-19 infected patients.

Methods: A retrospective study was performed in 70 asymptomatic COVID-2019 infected patients confirmed by nucleic acid tests in Hunan province, China between 28 January 2020 and 18 February, 2020. The epidemiological, clinical features and laboratory data were reviewed and analyzed. Presence or absence at the onset of symptoms was taken as the outcome. A Cox regression model was performed to evaluate the potential predictors of the onset of symptoms.

Results: The study included 36 males and 34 females with a mean age of 33.24±20.40 years (range, 0.5-84 years). There were 22 asymptomatic carriers developed symptoms during hospitalization isolated observation, and diagnosed as confirmed cases, while 48 cases remained asymptomatic throughout the course of disease. Of 70 asymptomatic patients, 14 (14/70, 20%) had underlying diseases, 3 (3/70, 4.3%) had drinking history, and 11 (11/70, 15.7%) had smoking history. 22 patients developed symptoms onset of fever (4/22, 18.2%), cough (13/22, 59.1%), chest discomfort (2/22, 9.1%), fatigue (1/22, 4.5%), pharyngalgia (1/22, 4.5%) during hospitalization; only one (1/22, 4.5%) patient developed signs of both cough and pharyngalgia. Abnormalities on chest CT were detected among 35 of the 69 patients (50.7%) after admission, except for one pregnant woman had not been examined. 4 (4/70, 5.7%) and 8 (8/70, 11.4%) cases showed leucopenia and lymphopenia. With the effective antiviral treatment, all the 70 asymptomatic infections had been discharged, none cases developed severe pneumonia, admission to intensive care unit, or died. The mean time from nucleic acid positive to negative was 13.2±6.84 days. Cox regression analysis showed that smoking history (P=0.028, hazard ratio=4.49, 95% CI 1.18-17.08) and existence of pulmonary disease (P=0.038, hazard ratio=7.09, 95% CI 1.12-44.90) were risk factors of the onset of symptoms in asymptomatic carries.

Conclusion: The initially asymptomatic patients can develop mild symptoms and have a good prognosis. History of smoking and pulmonary disease was prone to illness onset in asymptomatic patients, and it is necessary to be highly vigilant to those patients.

Keywords: COVID-19, asymptomatic infected patients, symptoms onset, risk factors, predictive value