Though the presence of epidemics and pandemics has plagued humanity for centuries, infectious disease transmission remains poorly understood. The classification of transmission of disease continues to rely on notions of routes of transmission introduced in the 1930s. Although contact tracing aiming at gathering data from survey of populations and tracking case reports to infer routes of transmission are also now more accessible, the biases and accuracy such Big Data sets are difficult to assess. Hence, further limiting our understanding the mechanisms of contagion. There remain a major knowledge gap between the results in basic microbiology performed at the cellular scale (e.g., how does one virus infect one cell) and the attempts to model contagion and patterns of epidemic spread at the population level. Dr. Lydia Bourouiba, Esther and Harold E. Edgerton Assistant Professor Director of the Fluid Dynamics of Disease Transmission Laboratory at the Massachusetts Institute of Technology, is using her research to fill this gap and connect the small scales to the population scale. In particular, Dr. Bourouiba focuses on understanding how the pathogens of one individual become those of another. Using a unique combination of methods that join physical sciences, including fluid dynamics, with microbiology and epidemiology, Dr. Bourouiba examines the dynamics of peer-to-peer transmission and transport of pathogens in the air and water, with implications on transmission of diseases in an office, airplane, hospital, or any public spaces. The insights gained will enable better risk assessment, improved and targeted intervention and mitigation strategies and better design of spaces and protective equipment in healthcare settings.  

Dr. Bourouiba and her team of scientists collaborate with other U.S. and European researchers, as well as members of the medical community, to explore the universal process of disease transmission. They study fluids—droplets in the air we breathe and on contaminated surfaces—and their role as transporter, carrying pathogens from one location to another. By linking information at this mesoscale, Dr. Bourouiba and her team will be able to improve prediction of patterns of outbreaks and how to concretely design intervention strategies indoors, especially for healthcare workers and in time of epidemics and pandemics. 

The ongoing experiments in The Fluid Dynamics of Disease Transmission specifically focus on respiratory disease in humans, with plans to use animal models also, as proxy to study influenza transmission. They also examine pathogen spread in agricultural fields also mediated by water drops. This is the case rain-induced rust transmission in crops such as wheat, coffee, or citrus, for which rust continue to lead to major crop yield loss. The group also focuses on water-borne diseases, air contamination from water sources, and on nosocomial diseases; in other words, diseases acquired and spread in hospitals. The vision Dr. Bourouiba is to leverage the physical sciences—fluid dynamics in particular—to root epidemiology modeling, contagion risk assessment, and mitigation strategies in mechanistic understanding of transmission. As the number of world-wide outbreaks and epidemics of emerging and re-emerging diseases continue to strike our inter-connected societies, this emerging area of research will shed light on critical unknown processes shaping the chain of transmission and epidemic patterns. 

Current projects include:

• Respiratory diseases – The classification of the dominant route of transmission of infectious diseases is important as it determines the resource allocation and intervention strategies deployed in the field by health organizations.  The classification of respiratory disease transmission heavily rely on a physical picture from the 1930s describing respiratory emissions in terms of large or small droplets. Dr. Bourouiba’s research showed that this physical picture required revisiting. Indeed, when we cough or sneeze, violent expirations do not merely emit a large or small droplets, but they emit a continuum of sizes suspended in a multiphase turbulent gas cloud of fluid. Her findings also showed that the current physical picture under-estimate the range of contamination significantly. Indeed, this cloud extends the range of contamination and can protect the pathogens carried in the respiratory droplets. Dr. Bourouiba’s studies create a physical description of this process, enabling a full description of both temporal and spatial spread of contamination. Dr. Bourouiba and her team are working on multiple projects in this area, which include understanding the physics behind the creation of respiratory droplets.
• Nosocomial diseases  - Superbugs in hospitals are an increasing public health concern. Similarly to the violent expirations in respiratory flows, Dr. Bourouiba is studying the various ways contaminated water droplets are emitted in a range of hospital settings, such as in toilet flushes collocated  in the vicinity of patient’s bed. Control measures in hospitals currently focus on chemical surface decontamination. Unfortunately, this only  addresses droplets that settle on such surface. The current work of Dr. Bourouiba focuses on assessing how much of such droplets are likely to settle in comparison to those that will remain suspended; how are they formed, and how much contaminants do they contain. Her research focuses on elucidating the physical mechanisms of such process of droplet creation and contamination in order to enable control and design of novel tools or protocols for mitigation of  contamination.
• Foliar Disease Transmission - With a growing population comes the need for more food. However, crop diseases are also on the rise, with wheat rust for example being coined, the “plague” of agriculture in recent years. Adopting similar principles from human epidemiology, Dr. Bourouiba and her team are using fluid dynamics and  surface science to study the transmission process of crop pathogens between plants during rainfall or irrigation. They are also investigating redesign the chemical sprays and optimization of field planning to mitigate spread once one plant is infected.
• Water-borne diseases - In the ocean, bubbles enable the transport of chemicals and minerals from the water to the air. Considering bubbles the “missing link”, Dr. Bourouiba investigate the role of bubble bursting producing harmful droplets from contaminated water. Taking her research indoors, she looks at the transport of pathogens such as those from infected patients in wastewater or outdoors close to wastewater treatment facilities. Stemming from the understanding of the physical processes of such water-to-air contamination, proper control strategies and produce are being identified by her team.