Back-calculation and environmental modeling for the 2003 SARS epidemic and developing effective engineering control methods

The 2003 severe acute respiratory syndrome (SARS) epidemic was characterized by the occurrence of large clusterings (i.e. super-spreading events) of infections. Environmental factors were suspected to play significant roles in some of these large outbreaks. For determining the environmental factors, it is important to estimate the time of infection. Estimating the time of infection, an unobservable event per se is also important in determining the other key transmission parameters and epidemiological characteristics of emerging infectious diseases. We first discuss a back-calculation method for estimating time of infection and the daily number of infected cases. We compare the estimated solutions from our proposed method to those obtained by the widely used expectation maximization method, for a simulated data set and two empirical SARS data sets from the 2003 Hong Kong SARS epidemic. We then present a review of literature on the use of experimental and mathematical modelling of fluid mechanics in investigating the roles of building ventilation and air flow in some airborne diseases as well as developing new engineering control methods. The pros and cons of mathematical modelling in providing environmental investigations for large outbreaks of suspected airborne infectious diseases are discussed using the two example studies, i.e. the Amoy Gardens outbreak and the Prince of Wales Hospital 8A ward outbreak, and in studying ventilation systems in SARS isolation wards. A study of this nature needs an inter-disciplinary study with involvement of medical professionals, infection control experts, microbiologists, epidemiologists and engineers. Note: These lecture notes are written based on both published and unpublished materials from my research at the University of Hong Kong, in collaboration with various organizations. Please do not cite these materials without permission.