Ventilation Assessment and Airborne Transmission Risk of SARS-CoV-2 in Nursing Homes in Seosan, the Republic of Korea, 2025.

Objectives: This study quantitatively evaluated the levels of natural and mechanical ventilation in nursing homes and group homes in Seosan, the Republic of Korea, and estimated the airborne transmission risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (Delta variant) according to ventilation conditions, with the aim of emphasizing the need for improved ventilation in infection-vulnerable facilities. Methods: On-site investigations were conducted in 23 nursing homes and four group homes. Bedroom ventilation rates were directly measured, and air changes per hour (ACH) were calculated by using supply and exhaust airflow data and room volume. The Korea Disease Control and Prevention Agency airborne transmission risk assessment tool was also applied to estimate infection risk under a scenario involving one infectious SARS-CoV-2 Delta variant case and a 3-hour exposure period. Results: The average frequency of natural ventilation was 5.5±2.3 events per day, with a mean duration of 15.4±10.4 minutes per event. The mean total ventilation rate in bedrooms was 1.4±0.9 ACH. Only 11.1% of the facilities achieved ≥2 ACH through natural ventilation alone, while none achieved ≥2 ACH through mechanical ventilation alone. In the 19 facilities equipped with mechanical ventilation systems, combined operation with natural ventilation reduced the estimated infection risk by an average of 11.4±6.9%p relative to natural ventilation alone (95% confidence interval: 7.9-14.7). Conclusions: Reliance on natural ventilation alone is insufficient for mitigating airborne infection risk. Thus, enhanced design and operation of mechanical ventilation systems, together with the adoption of ACH-based standards and mandatory mechanical ventilation requirements, should be incorporated into evaluation criteria for long-term care facilities.