Massive Science on Lydia Bourouiba

TEDMED is proud to partner with Massive Science, a digital science media publication that brings together scientists and the science-curious public. The team at Massive joined us onsite at TEDMED 2018, and covered talks by various speakers including Lydia Bourouiba. Check out their coverage of Lydia’s TEDMED 2018 talk below.

In 1934, Williams Wells was the first scientist to convincingly describe airborne transmission of diseases in the context of tuberculosis. He introduced the notion of  two main routes of pathogens spread: large droplets, which fall due to gravity, and small droplets, which waft through the air as they evaporate. It is believed that pathogens like Tuberculosis are transmitted through large droplets, whereas diseases like measles could through small ones, although evidence remain controversial and debated. 

It may surprise you that for more than 80 years—despite new diseases, new means of travel, and new technology—our understanding of these basic routes haven’t changed much. Not until recently, when Lydia Bourouiba, associate professor at the Massachusetts Institute of Technology and director of the Fluid Dynamics of Disease Transmission Laboratory, began to revisit these fundamentals and redefine how we think about respiratory disease transmission—literally from the ground up.

Bourouiba began her career by studying the mathematics of how fluids flow, specifically looking at fluids with turbulent or chaotic dynamics/motion. When she moved to Toronto shortly after the SARS epidemic, she realized that similar mathematical principles could be useful in modeling how diseases spread. That’s when she began to use mathematics in epidemiology, and in particular, the limitations of top-down modeling with mechanistic understanding of the fundamental mechanisms governing the patterns observed. “I started seeing these gaps in understanding transmission in particular, and [seeing] that fluid dynamics could help fill such gaps,” explains Bourouiba.

Traditionally, scientists have created epidemiological models by developing equations, based on a variety of parameters that describe how diseases are transmitted between people and populations. However, many of these parameters are fitted to data and not based on physical principles—like how sneezing actually transmits disease, or what factors influence how far sneeze droplets may travel or persist. 

Bourouiba thinks that improving the accuracy of these parameters and framework of modeling would greatly improve predictive power and intervention strategies. “If one doesn’t have a mechanism to rationalize [the parameters] down to something we can directly measure, validate, and control, one ends up fitting data to models,” says Bourouiba, rather than designing models that incorporate underlaying physics. “One loses predictability power and ability to control.”

So Bourouiba moved to MIT as an NSERC Postdoctoral Fellow and Applied Mathematics Instructor, and then as faculty, and began to try to explain how diseases are transmitted globally based on how they are transmitted between you and your neighbor. Equipped with a range of experimental optical and biophysics methods, including, direct visualization and measurements, such as with high-speed imaging, microscopy, fluid flow models, and patients, Bourouiba and her team are now answering fundamental questions about the mechanisms of respiratory disease transmission.

During TEDMED, Bourouiba showed how the physics of turbulent puff cloud of air emitted during exhalations, suspending and trapping drops within them, radically  change the range of pathogen deposition and contamination, thus, shifting the paradigm away from the small versus large droplet framework of Wells into the mechanistic description of exhalations including information of time and space, needed for monitoring, infection control and prevention,  and risk assessments. 

The next step is understanding how a exhalations coupled with ambient environment and patient physiology in infection, including when infected with flu, can inform early detection and intervention.  Her broad findings have already identified suggestions for disease control that can be implemented, influencing a variety of public health protocols and policies.

But she still has further questions—like how the size of droplets can impact our susceptibility to disease. “The properties that exhalations and their payload influence also efficacy of infection upon exposure, for example influencing,  their deposition in the lungs,” says Bourouiba. “We are working at elucidating the whole process, accounting for coupled physiology, immunology, microbiology, and fluid processes, to construct the full picture of those  that have particularly high abilities to transmit certain respiratory diseases effectively.”

This could inform how we manage numerous high impact pathogens. Take tuberculosis, a disease that infects up to a third of the world’s population. Researchers know its symptoms begin deep in the lungs, but further characterizations of when, how, and why people produce infectious droplets could improve how we handle patient care and research.

Bourouiba is excited about the multi-year study she’s leading with a diverse collaborations she put in place to  include clinicians, infection control specialists, microbiologists, immunologists, and virologists, for the study of transmission of influenza. Pioneering work in this interdisciplinary field isn’t easy. But Bourouiba says that ten to twenty years of this kind of research could lead to dramatic, tangible results, useful for a variety of pathogens. Considering the long and often uncertain process of developing new vaccines and diagnostics for infectious diseases, her approach to defining evidence-based prevention strategies is a vital piece of the puzzle. “You have to be doing both [prevention and treatment research].” It’s also becoming ever more important. Because of rising antibiotic resistance and increase in connectivity, and emergence and re-emergence of pathogens, she explains, “We might be going into an era [similiar] to pre-antibiotic times, which is extremely concerning.”

Bourouiba’s work is an important step toward redefining disease transmission, and infection control and prevention, moving the fundamentals from descriptions to measurable and quantifiable mechanisms. Truly understanding how people get each other sick will help us design protocols, policies, and tools to help people stay healthy and prevent epidemics and pandemics.

About the author:  Joshua Peters is a PhD student in Biological Engineering at MIT. Around two billion people in the world are infected with a microscopic bug called Mycobacterium Tuberculosis. Despite this, only a fraction develop tuberculosis. And a fraction of those infected – almost 5,000 a day – die. Joshua puts on Stranger Things-esque protection equipment and probes these bacteria to ask, what allows them bacteria to win this tug-of-war? To understand this variation, he looks at how both human and bacteria cells change on a genetic level in response to each other, as a member of the Blainey Lab, located in the Broad Institute, and Bryson Lab, located in the Ragon Institute and MIT.