Researchers Unveil What Makes a Super Spreader COVID-19

Scientists and public health experts have long known that certain individuals, called “superspreaders”, can transmit COVID-19 with incredible efficiency and devastating consequences.

Now researchers at Tulane University, Harvard University, MIT and Massachusetts General Hospital have found that obesity, age and COVID-19 infection correlate with the propensity to exhale more respiratory droplets – the main disseminators of SARS-CoV-2, the virus that causes COVID-19. Their findings were published in Proceedings of the National Academy of Sciences.

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

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

Aerosol droplets in non-human primates increased as COVID-19 infection progressed, reaching peak levels one week after infection before returning to normal after two weeks. Notably, as the COVID-19 infection progressed, the viral particles decreased, reaching the size of a single micron at the peak of the infection. Tiny particles are more likely to be expelled when people breathe, speak or cough. They can also stay afloat for much longer, travel farther into 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 Chad Roy, Ph.D., corresponding author and director of infectious disease aerobiology at the Tulane National Primate Research Center.

“We saw a similar increase in droplets during the stage of acute infection with other infectious diseases like tuberculosis,” said Roy. “It seems likely that viral and bacterial infections of the airways can weaken mucus in the airways, which promotes the movement of infectious particles into this environment.”

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

“While our results show that young and healthy people tend to generate much less droplets than older and less healthy ones, they also show that any of us, when infected with COVID-19, may be at risk of producing a large number of respiratory droplets, “said Edwards.