The emergence and explosive spread of virulent viral (e.g. H1N1, SARS) and bacterial (e.g. Tuberculosis) infections is a problem of global interest with enormous human and economic consequences. Population and network disease models yield insight into, and guide policy aimed at mitigating, the spread of these public health threats. In such models, the central notion of contact greatly influences the disease epidemic outcomes, but its definition remains nebulous. This project clarifies the notion of contact through developing our understanding of the fluid dynamics of respiratory disease transmission. A hierarchy of mathematical models of increasing complexity are combined with analogue laboratory experiments to elucidate several fluid dynamics problems bearing directly on contact and disease spread. Specifically, this project elucidates the factors influencing the generation and transport of droplet-borne pathogens inside the respiratory tract, and their subsequent dispersal through the air via coughing, sneezing or normal breathing. Such models yield valuable insight into the range and efficacy of pathogen transport via exhalation and so guide policy on the management of infected patients in confined environments such as hospitals and airplanes.
This research highlights the key role played by fluid dynamics in disease transmission, and suggests novel approaches to open questions in the classical mathematical modeling of disease spread. One principal goal is to refine the quantification of contact as input for epidemiological models, thus improving their predictive accuracy. The research will also raise the bar on the mathematical modeling of airborne transmission, by drawing on established mathematical models of multiphase, multiscale interfacial flows to elucidate the factors influencing the likelihood of infection via bacteria- or virus-laden airborne droplets. The research can thus inform the modeling of contact in respiratory diseases in confined environments, and so guide policy for disease transmission in hospitals and airplanes. Finally, the project is transformative, bringing the mathematical framework of modern fluid dynamics to a new class of important biomedical problems. Through introducing these problems to the fluid dynamics community, as resides traditionally in applied mathematics, engineering and physics departments, it initiates an exciting branch of interdisciplinary science.
The emergence and spread of virulent viral and bacterial infections is a problem of global importance with enormous human and economic consequences. Mathematical models of disease spread within a population yield insight into, and guide policy aimed at mitigating, the spread of these public health threats. Our research was aimed at informing such models through developing a consistent fluid mechanical description of respiratory disease transmission via violent expiratory events. Guided by direct flow visualization of coughs and sneezes (see Figures 1 and 2) and analogue laboratory experiments, we developed a new physical picture of the flows accompanying violent expiratory events. The revised physical picture is that of a hot, buoyant gas cloud accompanied by potentially pathogen-bearing droplets, the largest of which fall out directly, the smallest of which can be suspended within the cloud for considerable distances. To describe these flows, we developed a hierarchy of mathematical models of increasing complexity that capture the factors influencing the generation, transport and dispersal of droplet-borne pathogens. Such models yield valuable insight into the range and efficacy of pathogen transport via exhalation, and so may guide policy on the management of infected patients in confined environments such as hospitals. Mathematical models were developed to characterize the `pathogen footprint’ that surrounds an infected individual. Our results demonstrate that neglecting the dynamics of the gas phase responsible for the suspension of smaller droplets can result in an underestimation of the range of contamination by a factor of more than 200. Our results also allow us to relate the range of contamination to the environmental conditions through the quantification of the role of ambient moisture. Such insight informs the debate on the role of moisture in the range of contaminated cough or sneeze clouds. Another significant result from our research was the elucidation of the rich set of fluid dynamical processes that determine the final drop-size distribution (e.g. Figure 2). Our state-of-the-art flow visualization study revealed that a myriad of fluid fragmentation processes, previously associated with industrial flows, also accompany violent respiratory events. Our study indicates that, through determining the drop-size distribution, these fragmentation processes also ultimately prescribe the pathogen range. Our study has highlighted the key role of fluid dynamics in disease transmission, and suggests novel approaches to open questions in the mathematical modeling of disease spread. Our research has been transformative in bringing the mathematical framework of modern fluid dynamics to the problem of respiratory disease transmission, thereby contributing to the relatively new field emerging at the interface of fluid dynamics and health care.
