Inhalation exposure assessment techniques on ventilation dilution of infectious respiratory particles in a retrofitted hospital lung function room

Abstract

Controlling the spread of respiratory infections in healthcare settings is important to prevent nosocomial infections. To assess the effectiveness of commonly used techniques in the hospital for evaluating the performance of building retrofit to reduce the risk of nosocomial infection, we employed computational fluid dynamics (CFD) simulation, real-time carbon dioxide (CO2) monitoring, microorganism culturing, and microorganism sequencing. These techniques can quantitatively assess the direct and indirect inhalation exposure risk of healthcare workers (HCWs) to infectious respiratory particles (IRPs) exhaled by patients in a hospital lung function room under two ventilation configurations. Originally, the ventilation system provided 2 air changes per hour (ACH) for clean air and 2 ACH for recirculated air. After retrofitting, the ventilation system was modified to increase clean air to 6 ACH and remove recirculated air. However, the assessment techniques yielded conflicting results regarding the percentage differences in exposure risk before and after the retrofit. The findings indicated that the retrofit system reduced indirect inhalation exposure risk, as estimated by real-time CO2 monitoring and microorganism culture, by over 50.00%. However, the CFD simulation indicated an increase in inhalation exposure risk when 6 ACH of clean air was supplied. These results suggest that removing recirculated air and increasing the air change rate are effective in reducing long-range indirect inhalation exposure in the lung function room. However, they are insufficient to minimize the direct inhalation exposure of patients exhaling IRPs in close proximity. Given the conflicting results obtained from the commonly accepted techniques used in our study, it is necessary to provide a better understanding of infection control associated with the ventilation dilution of IRPs for hospital architects, hospital healthcare workers, and built-environment researchers.