Goals and Framework for EHMI Airborne Transmission of SARS-CoV-2 Virtual Workshop (4/36)

Brief talk by Jonathan M. Samet, MD, MS

Dean and Professor, Colorado School of Public Health

"We are here because this is a critical and important topic."

Tuberculosis was the top killer in the US near the beginning of the 20th century, and due to the belief that it was transmitted through salivia, campaigns were led against public spitting and spittoons. It was only after a clever study involving guinea pigs exposed to the exhaust air from a patient with tuberculosis that the theory of airborne droplet nuclei firmly took hold, and the authors are still frequently referenced for establishing this theory.


The last quote of this 1956 paper was: Those of us with a speculative turn of mind wonder whether air hygiene may advance as far in the next half century as water sanitation did in the last half century.

Dr. Samet goes on to say, "I think in fact that the need to have more scientific information about airborne transmission has revealed in fact how little progress we have made."

Framework adopted in a committee on research priorities for airborne particulate matter starting in 1998 that Dr. Samet chaired. They were charged with exploring uncertaintities around airborne particulate matter following controversies after the 1997 EPA National Ambient Air Quality Standards for Fine Particles (PM 2.5).

Framework adopted in a committee on research priorities for airborne particulate matter

Within this framework, people are the source of the airborne particles, which leads to infectious particles, whose exposure is stipulated by the the behavior of the built environment, leading to some degree of exposure, which may result in an infectious dose. This pathway has 4 key questions that the workshop will explore:

  1. What size particles are generated by people and how do they spread in the air?
  2. What size particles are infectious and for how long?
  3. What behavioral environmental factors determine personal exposure to SARS-CoV-2?
  4. What do we know about the infectious dose and disease relationship for COVID-19?

Overall workshop goal: To bring together relevant sectors of research and practice to explore and assess the evidence on airborne transmission of SARS-CoV-2 in order to indentify: 1) what we know; 2) what we need to know; 3) what research is needed to fill critical gaps; 4) in order to prevent and control infection with SARS-CoV-2 and COVID-19.

There are few papers on airborne transmission, but publications in this area have rapidly jumped in the past years, and also in the past months. While the volume of published papers is in the tens to hundreds, there are thousands of preprints on the subject awaiting peer review. Systemic reviews of existing research are underway and it is expected that the workshop will help identify gaps for further research.

The standard way that knowledge on micro-organisms is established is via the Henle-Koch Postulates, which are as follows:

  1. The micro-organism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
  2. The micro-organism must be isolated from a diseased organism and grown in pure culture.
  3. The cultured micro-ogranism should cause disease when introduced into a healthy organism.
  4. The micro-organism must be re-isolated from the inoculated diseased experimental host and identified as being identical to the original specific causative agent.

However, we need a different set of postulates in thinking about airborne transmission and the following criteria are proposed as an anolog to Koch's postulates:

  1. Collection of particles (in a particular size fraction) in air containing exhaled breath from a COVID-19 patient.
  2. Demonstration of viral RNA in the collected particles, matching the genotype of the patient's virus.
  3. Culture of virus to demonstrate that it is viable.
  4. Documentation that the collected virus causes disease in an animal model or cytopathic effects in a cell culture system.

It is noted that comments reflect individual insights rather than the position of the National Academies and that the workshop is not part of a consensus study.

Each question will have individual contributions followed by panel discussions.

Next: Importance of Understanding the Role of Airborne Transmission in COVID-19 (5/36)

Previous: COVID-19: Public Health and Scientific Challenges (3/36)

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Jonathan M. Samet is a pulmonary physician and epidemiologist and is currently Dean of the Colorado School of Public Health. Dr. Samet’s research has focused on the health risks posed by inhaled pollutants and tobacco. He has served on numerous committees concerned with public health and the environment: the U.S. EPA Science Advisory Board; committees of the National Academies, including chairing the Biological Effects of Ionizing Radiation VI Committee, the Committee on Incorporating 21st Century Science in Risk-Based Evaluations, the Committee on Research Priorities for Airborne Particulate Matter, the Committee to Review EPA’s Draft Integrated Risk Information System Assessment of Formaldehyde, the Committee to Review the IRIS Process, and the Board on Environmental Studies and Toxicology, among others; and the National Cancer Advisory Board. He is a member of the National Academy of Medicine. Dr. Samet received his MD from the University of Rochester, School of Medicine and Dentistry and his master’s degree in epidemiology from the Harvard T.H. Chan School of Public Health.

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