Estimation of exposure levels of virus - Laden expiratory aerosals in a hospital ward under imperfect mixing condition

This study investigated the feasibility of using the spatial distribution of expiratory aerosols and the percentage viability of airborne viruses to estimate the spatial exposure levels of airborne viruses in rooms under imperfectly mixed condition. Experiments were conducted in a hospital ward with ceiling-mixing type ventilation system. A broth solution with a known concentration of bacteriophages, as to simulate airborne viruses, was aerosolized with a droplet size distribution similar to human expiratories. Spatial distributions of these aerosols were measured using an aerosol spectrometer. The percentage viability of bacteriophages was obtained using in-situ biological air sampling by an Andersen sampler. The applicability of the proposed method was verified by comparing the estimated exposure levels with those measured directly by in-situ biological air sampling at selected locations. Reasonable agreement was found between the two sets of results. The proposed method was then used to estimate the exposure levels of patients and hospital workers in the ward. Estimated exposure levels were found to have significant spatial variations. The proposed method may be further developed into applications for analyzing airborne infection risk in imperfectly mixed indoor environments and the results would provide information for establishing working standards in hospitals for virus induced airborne disease prevention.