Study Participants and Data Collection
We retrospectively recruited a total of 50 patients with COVID-19 from January 22 to February 16, 2020, at the Fifth Medical Center of PLA General Hospital. All enrolled patients were confirmed to be positive for SARS-CoV-2 nucleic acid by real-time polymerase chain reaction. Twenty-six healthy individuals comprising doctors, nurses and researchers also stationed in the same hospital campus during the sample collection period were included as controls. The severity of COVID-19 was judged according to the guidelines for the diagnosis and management of COVID-19 patients (7th edition) by National Health Commission of China. Briefly, mild group (n = 18) included those present mild symptoms without pneumonia; moderate group (n = 19) present with fever, respiratory symptoms, and pneumonia; severe group (n = 13) included severe and critical ill cases. Severe cases are characterized by dyspnea, respiratory frequency ≥30/minute, blood oxygen saturation ≤93%, PaO2/FiO2 ratio < 300, and/or lung infiltrates greater than 50% within 24 to 48 h in pulmonary imaging. Critical ill cases refer to individuals that exhibited respiratory failure and required mechanical ventilation, as well as septic shock, and/or multiple organ dysfunction/failure that required monitoring and treatment in ICU. Our records indicated 2 out of 13 severe patients were on mechanical ventilation at the point of blood sample collection. Demographic, clinical, and laboratory radiological data were extracted from electronic medical records. Baseline characteristics and laboratory findings of COVID-19 patients and healthy controls were summarized in Tables 1 and S1–S3. The admission data of these patients were collected and checked independently by two physicians. The study was performed in accordance with the Declaration of Helsinki principle for ethical research. The study protocol was approved by Ethics Committee of the Fifth Medical Center of PLA General Hospital. Written informed consent was waived by the Ethics Committee of the designated hospital for emerging infectious disease.