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.