Ventilation characteristics in a hospital where a COVID-19 outbreak occurred in the winter of 2020

To clear the influences of ventilation performance on COVID-19 outbreaks in hospitals, the ventilation characteristics were investigated in a ward of an over-30-year-old hospital where a large outbreak occurred in the winter of 2020. At the early stage of the outbreak, nasal high-flow (NHF) was used in a treatment room for a week, and many patients stayed in multi-bed rooms during the outbreak. The viruses could expand not only with the infected staff or patients but also with the virus-contained air. To make an emergent ventilation measure plan, which the hospital requested, the actual performance of the air-conditioning and ventilation system and the ventilation characteristics were investigated using airflow volume meters, smoke testers, and a tracer gas CO 2 . The results of the measurements and the analysis showed the following. The ventilation rates had decreased to 30 % of the design value in the ward. The ventilation rate was decreased to 10 % in the treatment room where NHF was used, and the ventilation rates were decreased to 4–31 % in the rooms with six beds. The room doors were usually opened, and the opening had the effect of increasing the ventilation rate of the room. However, the virus-contained air could expand to the corridor and the other spaces. The air supply is stopped to keep room temperature at night, and the ventilation is thought to be very poor, especially if the doors are closed. Inadequate ventilation in the old buildings may have affected the hospital outbreak cases. It is essential to check the ventilation characteristics regularly, especially in old buildings. The result contributed to the administrative notice “The Emergent Ventilation Measures to Control COVID-19 in Hospitals” in April 2021 in Japan.