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Super-spreaders: Exhale increases with COVID-19 infection, age, and obesity

Scientists and public health experts have long known that certain individuals, termed "super-spreaders," can transmit COVID-19 with incredible efficiency and devastating consequences.

Now, researchers at Tulane University, Harvard University, Massachusetts Institute of Technology (MIT) and Massachusetts General Hospital have learned that obesity, age and COVID-19 infection correlate with a propensity to breathe out more respiratory droplets – key spreaders of SARS-CoV-2, the virus that causes COVID-19.

Using data from an observational study of 194 healthy people and an experimental study of non-human primates with COVID-19, researchers found that exhaled aerosol particles vary greatly between subjects. Those who were older with higher body mass indexes (BMI) and an increasing degree of COVID-19 infection had three times the number of exhaled respiratory droplets as others in the study groups.

Researchers found that 18% of the human subjects accounted for 80% of the exhaled particles of the group, reflecting a distribution of exhaled aerosol particles that follows the 20/80 rule seen in other infectious disease epidemics – meaning 20% of infected individuals are responsible for 80% of transmissions.

Aerosol droplets in non-human primates increased as infection with COVID-19 progressed, reaching peak levels a week after infection before falling to normal after two weeks. Notably, as infection with COVID-19 progressed, viral particles got smaller, reaching the size of a single micron at the peak of infection. Tiny particles are more likely to be expelled as people breathe, talk or cough. They can also stay afloat much longer, travel farther in the air and penetrate deeper into the lungs when inhaled.

The increase in exhaled aerosols occurred even among those with asymptomatic cases of COVID-19, said Dr Chad Roy, corresponding author and director of infectious disease aerobiology at the Tulane National Primate Research Centre.

The generation of respiratory drops in the airways varies between people depending on their body composition, said lead author Dr David Edwards, professor of the practice of biomedical engineering at Harvard University.

"While our results show that the young and healthy tend to generate far fewer droplets than the older and less healthy, they also show that any of us, when infected by COVID-19, may be at risk of producing a large number of respiratory droplets," Edwards said.

 

Study details
Exhaled aerosol increases with COVID-19 infection, age, and obesity

David A Edwards, Dennis Ausiello, Jonathan Salzman, Tom Devlin, Robert Langer, Brandon J Beddingfield, Alyssa C Fears, Lara A Doyle-Meyers, Rachel K Redmann, Stephanie Z Killeen, Nicholas J Maness, and Chad J Roy

Published in PNAS on 23 February 2021

Abstract
COVID-19 transmits by droplets generated from surfaces of airway mucus during processes of respiration within hosts infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. We studied respiratory droplet generation and exhalation in human and nonhuman primate subjects with and without COVID-19 infection to explore whether SARS-CoV-2 infection, and other changes in physiological state, translate into observable evolution of numbers and sizes of exhaled respiratory droplets in healthy and diseased subjects. In our observational cohort study of the exhaled breath particles of 194 healthy human subjects, and in our experimental infection study of eight nonhuman primates infected, by aerosol, with SARS-CoV-2, we found that exhaled aerosol particles vary between subjects by three orders of magnitude, with exhaled respiratory droplet number increasing with degree of COVID-19 infection and elevated BMI-years. We observed that 18% of human subjects (35) accounted for 80% of the exhaled bioaerosol of the group (194), reflecting a superspreader distribution of bioaerosol analogous to a classical 20:80 superspreader of infection distribution. These findings suggest that quantitative assessment and control of exhaled aerosol may be critical to slowing the airborne spread of COVID-19 in the absence of an effective and widely disseminated vaccine.

 

[link url="https://news.tulane.edu/pr/researchers-unravel-what-makes-someone-covid-19-super-spreader"]Tulane University material[/link]

 

[link url="https://www.pnas.org/content/118/8/e2021830118"]PNAS study (Open access)[/link]

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