This review article summarizes the strengths and limitations of the Wells-Riley and the dose-response models for risk assessment of respiratory diseases. Even with many efforts by various investigators to develop and modify the risk assessment models, some limitations still persist. This review serves as a reference for further development of infection risk assessment models of respiratory diseases. The Wells-Riley model and dose-response model offer specific advantages. Risk assessors can select the approach that is suitable to their particular conditions to perform risk assessment.

The transport and deposition of polydispersed expiratory aerosols in an aircraft cabin were simulated using a Lagrangianbased model validated by experiments conducted in an aircraft cabin mockup. Infection risk by inhalation was estimated using the aerosol dispersion data and a model was developed to estimate the risk of infection by contact. The environmental control system (ECS) in a cabin creates air circulation mainly in the lateral direction, making lateral dispersions of aerosols much faster than longitudinal dispersions. Aerosols with initial sizes under 28 µm in diameter can stay airborne for comparatively long periods and are favorable for airborne transport. Using influenza data as an example, the estimated risk of infection by inhalation are at least two orders of magnitude higher than the risk of infection by contact. An increase in the supply airflow rate enhances ventilation removal and the dispersion of these aerosols. It reduces the risk of infection by inhalation for passengers seated within one row and one column from the index patient but it increases the risk for passengers seated further away. The deposition fraction increases with aerosol size. The ECS supply airflow rate has insignificant impact on the deposition behavior of these large aerosols, making the impact on the risk of infection by contact insignificant. Comparatively, the contact behavior of passengers is highly influential to the contact infection risk. Passengers seated within one row from the index patient are subject to contact risks that are one to two orders of magnitude higher than are passengers seated further away.

The transport and removal characteristics of expiratory droplets at different supply airflow rates and "coughing" orientations were investigated both numerically and experimentally in a three-bed hospital ward setting. A Lagrangian-based particletracking model with near-wall correction functions for turbulence was employed to simulate the fate of the expiratory droplets. The model was tested against experimental droplet dispersion data obtained in an experimental hospital ward using Interferometric Mie Imaging and a light-scattering aerosol spectrometer. The change in airflow supply rate had insignificant effect on the transport and deposition of very large droplets (initial sizes ≥ 87.5 µm) due to the dominance of gravitational settling on these behaviors. Smaller droplets (initial sizes ≤ 45 µm) exhibited certain airborne behaviors. The effect of thermal plumes from heat sources was observed only when the supply airflow was low and when the droplet size was small, as observed in the vertical mixing patterns of the droplets of various sizes. Larger droplets tended to settle lower and lateral dispersion of the droplets became weak at the low supply airflow rate. The deposition characteristics for different surfaces in the room are described. The heat plumes seemed to obstruct small droplets from being deposited onto heated surfaces. More deposition was predicted in the lateral injection case compared with the vertical injection case. Adopting near-wall correction for turbulence in the model reduced the predicted deposition removal fraction by 25% for 1.5 µm droplets. This reduction became less significant for larger droplets due to the smaller dependence on turbulent diffusion in their deposition. NOMENCLATURECunningham correction factor