Three Questions: Common Vocabulary on How Infectious Diseases Spread | Massachusetts Institute of Technology News

On April 18, the World Health Organization (WHO) announced: new guidance Research on airborne disease transmission attempts to develop a consensus on the terminology used to describe the transmission of airborne pathogens.

Lydia Bourouiba, Director of the Disease Transmission Fluid Dynamics Laboratory and Fluids and Health Network at the Massachusetts Institute of Technology, Associate Professor in the Departments of Civil and Environmental Engineering and Mechanical Engineering at the Massachusetts Institute of Technology, and Core Member of the Institute for Medical Engineering Sciences served as part of the WHO expert team that developed the guidance. For more than a decade, Bourouiba's lab has been studying the fundamental physical processes underlying how infectious diseases spread from person to person.

New guidance from WHO provides new definitions of key terms related to the transmission of respiratory infections. This reflects an emerging common understanding of how respiratory infectious agents move from person to person. This means that infectious contaminants can be carried through a turbulent “puff cloud” of exhaled air in a range of droplet sizes, leading to exposure at varying distances.

Bourouiba's lab has pioneered this physical landscape, working closely with a variety of stakeholders over the years to ensure that public health guidance incorporates the latest science and to address emerging respiratory pathogens. We have strengthened our preparations.Mr Bourouiva said: Massachusetts Institute of Technology News About WHO's new guidance.

question: How did you become involved in creating these new guidelines?

answer: I have been researching exhaled air emissions for over 10 years. After the first SARS outbreak in 2003, I realized that the mechanisms by which respiratory pathogens are transmitted from one host to the next are essentially too random and occur over such short periods of time that they are not amenable to systematic investigation. I noticed that it is thought that there is. Therefore, the physical act of pathogen infection was relegated to a black box. But we also realized that it is fundamentally important to mechanistically understand these infectious events so that we can ultimately mitigate them in a rational and principled way. . This required an understanding of the fluid physics and biophysics of respiratory exhaust gases.

MIT's Disease Transmission Fluid Dynamics Laboratory has been investigating these respiratory emissions. Our study shows that previous guidelines, specifically the dichotomy of “large” and “small” droplets, and isolated droplet releases (essentially from spray bottles), are important when investigating respiratory releases. It has been shown that there is absolutely nothing that can be seen and quantified. We provide a complete understanding of such processes, from the physiology of expiration to the fluid mechanics and biophysics of exhaled flow, to the interaction of exhaled turbulent multiphase flow with ambient environmental conditions (airflow, temperature, humidity). Focused on establishing physics.

Since 2015, I have been working with the Policy Lab at the MIT Center for International Studies to disseminate our findings to public health officials and various institutions. We held multiple meetings before and during the pandemic with scientists, clinicians, virologists, epidemiologists, microbiologists, and representatives from the Centers for Disease Control and Prevention and other groups.

In 2022, I was asked to serve as part of the World Health Organization's Technical Consultation Expert Team, tasked with reaching agreement on a new framework for the transmission of respiratory infections. This process lasted approximately two years and culminated in the publication of new guidelines. This process has clearly been accelerated by the COVID-19 pandemic and the issues it has highlighted regarding inappropriate and outdated definitions. The purpose of convening this consultative group was to bring together leading experts from around the world in highly diverse fields, from fluid physics to clinical medicine to epidemiology, to discuss how to redefine terminology related to the transmission of respiratory infections. The idea was to consider what would be the best way to define it. Latest science. These new guidelines are just the first step in a series of important consultations and initiatives.

question: How has your research changed the WHO's explanation of how diseases are transmitted through the air?

answer: Our study demonstrated that these isolated droplets are not simply exhaled as isolated droplets moving semi-ballistically. [that will settle out of the air relatively near to the person who released them]. Instead, they are part of a multiphase turbulent puff gas cloud that contains a range of droplet sizes, and this cloud has a relative Provides a warm, moist, and therefore protective environment. One of his first papers establishing this concept was published in his 2014. And since then, we have shown that models that do not include the proper physics of these turbulent spray clouds significantly underestimate the extent of transmission and also completely change estimates of risk and pathogen persistence in the region. We have shown that it is possible. indoor space.

These turbulent puff clouds are heterogeneous and, in the case of the most vigorous exhalations, can move very quickly through indoor spaces while creating droplet load areas containing high concentrations of pathogens that can persist for relatively long periods of time. may exist. Their kinetics allows for potentially effective inhalation exposure over long and short ranges. This continuous, physical picture of concentrated droplet packets, and their impact on pathogen infectivity and duration of exposure, is important for the concept of homogeneous mixing indoors, as well as for “large” droplets that fall ballistically. This is in complete contrast to the previous false dichotomy of “tiny” droplets. These essentially evaporate quickly to form an aerosol that is considered inert. Previous circumstances have led to the idea that only a few infectious diseases are airborne or require air management. This dichotomy, along with other misconceptions, has its roots in 1930s science and surprisingly remains in guidelines for decades.

The new guidelines are a major milestone. Because not only do these guidelines change infrequently (every 10 or 15 years at most), but also because, in addition to the WHO, five national or transnational health organizations have already endorsed this finding. . The US Centers for Disease Control and Prevention also acknowledged the importance of this change.

question: What are the biggest impacts of these changes?

answer: A common, agreed-upon terminology is important for infectious disease research and mitigation. The new guidelines lay the foundation for such a common understanding and process. Some might think it's just semantics, or small incremental changes in our understanding. However, the actual risk calculations vary widely depending on the framework used. Using mathematical models and physical experiments, we found that changes in physical conditions have a dramatic impact on risk estimates.

Another big implication was discussed in one of our articles. Publication From the very early stages of the pandemic, there is an urgent need for healthcare workers to wear N95 masks due to this cloud movement and the associated importance of paying attention to indoor air management. I emphasized. Again, risk calculations that do not use spray cloud dynamics suggest that in a typical hospital room or emergency department, the pathogen load is sufficiently diluted to not pose a high risk. However, puff clouds and the movement of droplets of continuous size within them, coupled with that, have made it clear that healthcare workers can still be exposed to significant viral loads through inhalation. Therefore, N95 masks should have been provided in most situations when entering spaces containing COVID-19 patients, even if not in the immediate vicinity. This article was the first to call attention to the importance of masks for health care workers, as the continuity of actual exhaled breath puff clouds and droplet size constitutes airborne transmission.

It took more than six months for public health agencies to begin considering changes to mask-wearing guidelines during the coronavirus pandemic. But this WHO document is broader than COVID-19. It redefines the fundamental definitions surrounding all respiratory infections, what we know and what will happen. This means that there are different risk assessments, and therefore different decision-making trees and policies, different choices of protective equipment and mitigation protocols, and different parts of health organizations and facilities that may be activated or deployed. It means that it spreads to

The new guidelines demonstrate that infectious disease transmission is a truly multidisciplinary field, and that scientists, clinicians, and public health officials from different backgrounds, whether in basic physics or clinical infectious diseases, can communicate effectively and clearly with each other. It is also an important recognition that insights need to be shared. disease. Therefore, not only the content of these guidelines is important, but also how this update is deployed. I hope that it will change the way we think about responding to public health threats like this.