Disinfection effectiveness of UR-UVGI for airborne bacteria based on equivalent air change rate in a multi-bed patient room

The prevention of airborne infectious disease transmission in indoor spaces is closely linked to maintaining healthy environments and indoor air quality (IAQ) for occupants. In particular, multi-bed hospital rooms require special attention, as they present higher risks of cross-contamination through bioaerosol dispersion. Ultraviolet Germicidal Irradiation (UVGI) has been recognized as an effective method for microbial inactivation, and its application in healthcare settings offers potential for both infection control and IAQ management. This study evaluates the disinfection performance of Upper-Room UVGI systems in a four-bed patient room mock-up. Bioaerosols were released from a 6-jet nebulizer at one bed to simulate a localized source. Airborne bacteria were sampled at three other beds (representing patient breathing zones) and at the end-terminal of the air handling unit (AHU). Experiments were conducted under 2 and 6 h−1, and three UR-UVGI operational conditions (off, one system on, two systems on). To quantify the UR-UVGI performance, the equivalent air change rate (eACH) was calculated based on the decay of airborne bacterial concentrations over time. In the AHU end-terminal, the eACH under UV off conditions was found to be higher than the set ventilation rate, with values of 7.58 h−1 (set 6 h−1) and 4.85 h−1 (set 2 h−1). UR-UVGI operation increased eACH by approximately 1 h−1 at the AHU. In the patient room, UR-UVGI operation led to more significant eACH increases. For the 6 h−1 condition, eACH rose from 6.3 h−1 (UV off) to 8.6-9.0 h−1 (UV on), and for the 2 h−1 condition, from 3.7 h−1 to 5.4-5.5 h−1. These results confirm the disinfection effect of UR-UVGI within the room; however, discrepancies at the AHU terminal suggest potential influences from surface deposition and duct-related losses. Additionally, variations in eACH were observed depending on the sampling and UR-UVGI locations, suggesting that airflow distribution and environmental factors should be considered. This highlights the need to assess local ventilation and infection risks near each patient. This study suggests that eACH estimation based on airborne bacterial decay is a valid method for evaluating UR-UVGI effectiveness and can be improved further by accounting for bioaerosol behavior and airflow characteristics.