Relative effectiveness of ventilation in community indoor environmentsfor controlling infection

The existence, probability and control measures of airborne infections have been widely discussed for centuries. Although public belief regarding airborne infection kept on altering throughout the entire history of medicine and is still controversial, many airborne transmission experiments and airborne infection outbreak analyses have been carried out. Different airborne transmission models have been built and various airborne control measures have been evaluated. One of the major knowledge gaps obstructing applications of some airborne control measures in clinical practices and public applications is that there is a lack of evidence in proving the effectiveness of such measures. Ventilation as an important airborne infection control method can be achieved by opening windows, or increasing the outdoor air supply rate in mechanical ventilation systems or indirectly by using filters and ultraviolet equipments. However the applications of ventilation in infection control were largely restricted to isolation rooms rather than regarded as a public control measure. In this study we focus on evaluating the effectiveness of ventilation as a community measure. Results, therefore, can provide evidence for using ventilation as a public health measure for controlling respiratory diseases transmitted by the airborne route or multi-routes. Two mathematical modeling approaches (deterministic model and social network model) are adopted to estimate different airborne diseases outbreaks with a focus on ventilation and a corresponding analysis of their relative effectiveness compared with other public health measures. A comprehensive understanding of detailed control strategies (including both engineering and public health control) will be achieved through gradually complicated and realistic models. It’s commonly believed that many respiratory infections are transmitted through multiple routes including airborne, droplet-borne and contact routes. Hence the effectiveness of airborne control measures was doubted when the airborne route was not dominant. Therefore, we developed a model to simulate partially airborne transmitted diseases outbreaks and evaluated the relative effectiveness of ventilation when the role of airborne transmission altered. Knowing the complex transmission mechanisms of respiratory transmission and the role of the airborne route in the transmission process is essential in determining the effectiveness of airborne control measures. Hence in this study we also tested the virus exposures dose to infectious patients at different distances when patients were carrying out different respiratory activities. A complex model considering transmission mechanisms of respiratory infections was also built to evaluate the influence of the transmission route in large scale outbreak simulations. The results showed that increasing ventilation rate especially in homes, offices and classrooms is an effective control method for controlling airborne and partially airborne transmitted infections. Combining isolation and increasing ventilation rate can reach similar or even better control effect compared with other general public health interventions such as vaccination. This finding suggested the important role of ventilation in airborne infectious disease prevention and intervention. The ventilation rate required by existing ventilation standards such as ASHRAE 62 might be too low for the purpose of controlling possible airborne outbreaks.published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph