Effectiveness of Upper-Room Ultraviolet Germicidal Irradiation on Airborne Bacteria Concentration in Full-Scale Airborne Infection Isolation Rooms

Abstract

The SARS-CoV-2 pandemic has highlighted the importance of maintaining a healthy indoor environment, particularly in healthcare facilities where strict infection control is essential. Airborne infection isolation rooms (AIIRs) are designed to isolate infectious patients and prevent the spread of airborne pathogens. However, additional microbial contamination control measures are necessary to ensure safe indoor air quality for both healthcare workers and patients. In this study, the disinfection performance of upper-room ultraviolet germicidal irradiation (UR-UVGI) was experimentally evaluated in a full-scale AIIR environment. Experiments were conducted under the AIIR minimum operational conditions (i.e., >= 6 air changes per hour (ACH)), using Bacillus subtilis (ATCC 6633) as the microbial contaminant. To simulate practical conditions, two microbial source scenarios were considered: (1) outdoor sources, wherein the microbes infiltrated from the anteroom into the ward, and (2) indoor sources, wherein the microbes were generated directly at the patient's respiratory position. The results indicate that for outdoor sources, UR-UVGI reduced airborne contaminants by approximately 20% at the ward center and 28% at the patient's respiratory position, but these reductions were not statistically significant (p > 0.05). By contrast, for indoor sources, UR-UVGI achieved a statistically significant reduction of approximately 23% at the ward center and 25% at the ward exhaust (p < 0.05). These findings suggest that UR-UVGI serves as a supplementary disinfection method in AIIRs. In addition, the relatively low disinfection efficacy observed at high ventilation rates (>= 6 ACH) indicates the need for optimized UR-UVGI placement strategies to enhance disinfection performance. Future research will focus on microbial dispersion and deposition patterns, incorporating computational fluid dynamics modeling to assess UR-UVGI effectiveness under various environmental conditions.