Estimation of exposure level and infection risk of airborne virus in indoor environment

A method used to estimate the exposures of airborne virus in indoor environment and analyze the subsequent infection risk had been developed in this research. The method utilized the spatial distribution of expiratory aerosols and the viability functions of airborne viruses carried in expiratory aerosols to estimate the exposures of airborne viruses in indoor environments that normally come with imperfectly mixed condition. Such approach was verified in a hospital ward with ceiling mixing type ventilation system. Artificial coughs were produced by aerosolizing a simulated human respiratory fluid containing a known concentration of benign E. Coli bacteriophage, as to simulate airborne viruses in disease transmission. Biological air sampling was performed at selected locations of the ward to obtain the bacteriophage viability function. Spatial distributions of the expiratory aerosols were measured by aerosol counting with an aerosol spectrometer. The estimated bacteriophage exposures were in reasonable agreement with those measured directly by biological air sampling. Bacteriophage exposures were also examined in the ward under occupied conditions using the proposed method. The ventilation flow pattern and coughing orientation played significant roles in the transport of expiratory aerosols, leading to different exposure distribution patterns. The proposed exposure estimation method was further incorporated into a dose-response model for infection risk assessment. Variations in infectivity by the carrier aerosol size were considered. Infection risk of an airborne transmission disease as in a general hospital ward at various locations were estimated by plugging the aerosol counting data obtained in the experiments together with epidemiology data. The results revealed the spatial variations of infection risk inside the ward, in which the existing infection risk analysis models are often failed to evaluate. The proposed method developed in this research may serve as a tool for further investigation of ventilation design and infection control in clinical or other indoor environments