Data collection
The information collected for COVID-19 patients included demographic characteristics (age, sex and continent), comorbidities (hypertension, diabetes, etc.), drug therapy, severity, clinical symptoms (fever, dry cough, expectoration, myalgia, diarrhea, shortness of breath, fatigue, etc.), radiological examinations (CT), and blood examinations (white blood cell count, lymphocyte cell count and lymphocyte cell percentage) at the first admission. The second admission information of positive retest patients was also collected. The information collected for close contacts included demographic characteristics, quarantine site (health care facilities and home), frequency of contact (often, moderate, and occasional), and contact modes (household, public transportation, health care settings, workplaces, and entertainment places).