Who are the super-contaminators, these infected people responsible for tens of direct contaminations and thousands of cases of covid? A new study published in the scientific journal Proceedings of the National Academy of Sciences (PNAS) in February 2021 draws a portrait of the people most at risk of massively infecting those around them.

According to researchers from the American universities of Tulane, Harvard and Massachussets General Hospital who signed the study, age and weight are important criteria. But the temporality of the infection would also play a role.

Read also: Covid: the “super-contaminators”, the main culprits of the pandemic?

High age and BMI

In a first experiment, the researchers analyzed the content of the exhalations of 194 healthy volunteers. They found that exhaled particles varied a lot from subject to subject.

Thus, the oldest who had the highest body mass indices (BMI) exhaled three times more droplets than the others. Specifically 18% of the human participants alone accounted for 80% of the exhaled particles in the group. This means that if these volunteers were sick, 20% of them would be responsible for 80% of the transmissions.

A peak at one week of infection

The researchers then carried out a second experiment, this time on primates (rhesus macaques and green monkeys) infected with the coronavirus. They then observed that the expired droplets increased as the infection progressed. The level peaked one week after infection, before falling back to normal at two weeks.

And the droplets also got smaller, reaching the size of a micron (100 times smaller than the diameter of a hair) at the height of the infection. However, the smaller the particles, the longer they stay in suspension in the air, the further they travel and the deeper they penetrate into the lungs when inhaled.

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In summary, according to this study, the typical profile of the super-contaminator is an elderly person, overweight, infected for a week.

Teeth and nose matter too

And if we add to these results those of a previous study in November 2020 in the journal Physics of Fluids, the portrait of super-contaminators is even more complete. According to researchers at the University of Florida at Orlando who published this publication, people with blocked noses and full teeth emit droplets that go deeper than other people, especially when they sneeze.

The complete typical profile of the super-contaminator is then an elderly person, overweight, infected for a week, who has a blocked nose … and all his teeth!

The only solution against contaminators, great or not: cough and sneeze into your elbow and wear a mask to limit the spread of droplets in the air.