Ventilation strategies based on an aerodynamic analysis during a large-scale SARS-CoV-2 outbreak in an acute-care hospital

BACKGROUND: This study aimed to investigate ventilation strategies to prevent nosocomial transmission of coronavirus disease 2019 (COVID-19). METHODS: We conducted a retrospective epidemiological investigation of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak in a teaching hospital (February–March 2021). The largest outbreak ward was studied, and measurements were taken to determine the pressure difference and air change per hour (ACH) of the rooms. Airflow dynamics were assessed using an oil droplet generator, indoor air quality sensor, and particle image velocimetry in the index patient's room, corridor, and opposite rooms, by varying the opening and closing of windows and doors. RESULTS: During the outbreak, 283 COVID-19 cases were identified. The SARS-CoV-2 spread occurred sequentially from the index room to the nearest room, especially the opposite. The aerodynamic study demonstrated that droplet-like particles in the index room diffused through the corridor and the opposite room through the opening door. The mean ACH of the rooms was 1.44; the air supply volume was 15.9% larger than the exhaust volume, forming a positive pressure. Closing the door prevented diffusion between adjacent rooms facing each other, and natural ventilation reduced the concentration of particles within the ward and minimised their spread to adjacent rooms. CONCLUSIONS: Spread of droplet-like particles between rooms could be attributed to the pressure difference between the rooms and corridor. To prevent spread of SARS-CoV-2 between rooms, increasing the ACH in the room by maximising ventilation and minimising the positive pressure through supply/exhaust control and closing the room door are essential.