Patients classification
Patients were classified into asymptomatic, presymptomatic, and symptomatic groups based on the retrospective review of the medical records. Asymptomatic COVID-19 patients were those with SARS-CoV-2 nucleic acid test positive but without any clinical symptom or only with stable pre-exist chronic symptoms (e.g., chronic cough without worsening). Presymptomatic patients were those asymptomatic inpatients on admission but then developed typical (fever, cough, shortness of breath) or atypical symptom (14, 15). Symptomatic patients were those who had typical clinical symptoms on admission.
The diagnosis and severity degree of each patient was determined according to the clinical classification criterion in Diagnosis and Treatment Protocol for Novel Coronavirus Pneumonia released by the National Health Commission (6th or 7th edition). In clinical, patients were classified into mild or moderate, severe, and critical cases, depending on the above criterion. In our analysis, the clinically defined severe or critical COVID-19 patients were grouped into severe cases group, and the clinically defined mild or moderate COVID-19 patients were defined as non-severe group cases.