1.1 Patients
In order to identify asymptomatic individuals, the Disease Control and Prevention (CDC) of Loudi conducted total of 1,844 close contacts (mean age 38.2± 19.9 years old), including 1,003 males (mean age 38.7 ± 19.9 years old) and 841 females (mean age 37.7 ± 20.0 years) with 76 confirmed patients with COVID-19 from January to May 2020. Nasopharyngeal swabs were collected for SARS-CoV-2 nucleic acid detection from all close contacts. Participants then submitted to a 14-day medical quarantine observation period. Asymptomatic cases who received two consecutively negative nucleic acid tests after the expiration of medical quarantine were observed at home for an additional 14 days. Asymptomatic cases were defined by a positive result from SARS-CoV-2 nucleic acid detection of respiratory tract specimens or serum specific IgM antibodies without corresponding clinical symptoms of COVID-19 in close contacts, based on the diagnostic criteria for COVID-19 and the requirements of the treatment plan (trial version 6 and trial version 7) issued by the National Health Commission of the People’s Republic of China and National Administration of Traditional Chinese Medicine [4, 5].
26 cases without clinical symptoms within 28 days of observation were recruited from close contacts following a positive SARS-CoV-2 nucleic acid detection. Close contacts whose nucleic acid test results were negative continued to be isolated for additional 14 days observation. 50 cases of healthy individuals from the First Hospital of Hunan University of Chinese Medicine served as the control group. Age and gender distribution did not differ between the study group and the control group (p>0.05). The details information of cases was presented in the results section. This study was approved by Ethics Committee of the First Hospital of Hunan University of Chinese Medicine.