ABSTRACT As COVID‐19 spread worldwide, numerous outbreaks occurred in wards. This study, in addition to investigating the indoor air environment and ventilation characteristics of a ward that had experienced multiple outbreaks, quantitatively evaluated how ventilation characteristics and door operation affect infection risk. Supply and exhaust airflow rates were measured, and ventilation characteristics—including air changes per hour (ACH) in each patient room, the supply–exhaust airflow balance, and ward ventilation pathways—were investigated. Furthermore, assuming the presence of a single index case, computational fluid dynamics (CFD) simulations were performed for four cases combining two airflow conditions and two door‐operation conditions, and the probability of infection under 24 h of exposure was calculated. The results confirmed a substantial ward‐wide decrease in supply airflow, indicating that outdoor air was not sufficiently supplied to patient rooms, and CO 2 concentrations exceeded 1,000 ppm at some measurement points. While poor ventilation facilitated the dispersion of infectious respiratory particles (IRPs) and increased infection risk, closing doors suppressed IRP dispersion and markedly reduced infection risk. Therefore, checking equipment conditions during normal operation and performing maintenance as needed, together with door operation according to the risk of nosocomial infection, are recommended for infection control in wards.
Tanaka et al. (2026) studied this question.