Why are some people infected with Covid-19 likely to be more contaminating than others? For researchers who have looked into the question, it all comes down to a combination of factors such as age, BMI and degree of infection.
- 20% of Covid-19 patients are said to be “super-contaminators”, responsible for 80% of infections.
- Elderly patients with higher body mass index and increasing degree of Covid-19 infection would exhale three times more droplets than other patients.
Last October, The voice of the North reported that in Hauts-de-France, a health center became a Covid-19 cluster in a few days. In question, according to the health authorities: an individual with a very high viral load who would have infected 53 people, including 29 staff members.
But who are these “super-spreaders” who exhale more respiratory droplets and are therefore more likely than other patients to spread SARS-CoV-2?
A study by researchers from Tulane University, Harvard University, MIT and Massachusetts General Hospital provides some answers. Published in Proceedings of the National Academy of Sciencesit shows that certain factors such as obesity, age and degree of infection correlate with a propensity to further contaminate those around you.
20% of patients responsible for 80% of transmissions
To reach this conclusion, the researchers used data from two studies: a first observation of 194 healthy people and a second experimental on non-human primates with Covid-19. By analyzing the data from the first study, the researchers found that exhaled aerosol particles vary greatly from subject to subject. Older participants with higher body mass index (BMI) and increasing degree of Covid-19 infection had three times more exhaled respiratory droplets than others in both study groups.
Furthermore, they noticed that only 18% of the human subjects accounted for 80% of the exhaled particles of the group. This means that 20% of infected people are therefore responsible for 80% of transmissions.
Smaller virus particles at height of infection
In primates, aerosol droplets increased as Covid-19 infection progressed, reaching peak levels one week after infection before falling back to normal after two weeks. The researchers especially noted that as the infection with Covid-19 progressed, the virus particles became smaller, reaching the size of a micron at the height of the infection. These tiny particles are more likely to be expelled when people breathe, talk or cough. They can also stay airborne much longer, travel farther, and penetrate deeper into the lungs when inhaled.
Interestingly, this increase in exhaled aerosols also occurred in asymptomatic people.
According to David Edwards, professor of biomedical engineering practice at Harvard University and co-author of the study, the generation of respiratory droplets in the airways varies from person to person depending on their body composition. .
“While our results show that young, healthy people tend to generate significantly fewer droplets than older, less healthy people, they also show that each of us, when infected with Covid-19, may be at risk of producing a large number of respiratory droplets”he concludes.
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