COVID-19(2) positive(2) SARS-CoV-2(2) Blood(1) clinician(1) addition(1) anesthesiologists(1) the SARS-CoV-2(1) without symptom(1) spring(1) initial(1) Infection(1) protocol(1) provided(1) IgG antibody(1) Clinical outcome(1) Physicians(1) PPE(1) patients(1) Safe(1) Preoperative medicine(1) HCW(1) Preparing(1) prevalence of COVID-19(1) 95% CI(1) while(1) antibody(1) Personal protective equipment(1) proportion(1) Humoral immunity(1)