Covid-19: it spreads more easily by talking than by coughing

In a new British study published in the journal Proceedings of the Royal society, researchers from the University of Cambridge (Great Britain) used a mathematical model to study how covid-19 spreads inside a room as a function of its volume, the number of people inside, its ventilation and of course the wearing (or not) of the mask.

The results of their study show that when two people are in a poorly ventilated space and not wearing a mask, having a prolonged conversation is much more likely to spread the virus than coughing. When we speak, we emit small droplets that spread and can remain suspended in the air. While coughing results in the production of larger and heavier droplets, which fall quickly to the ground or surfaces, and are therefore less easily inhaled.

A virus that is more easily transmitted in closed places

Last October, the U.S. Centers for Disease Prevention and Control updated their recommendations on the modes of spread of the coronavirus, emphasizing the potential for airborne spread. In this update, they raise the possibility of transmission of the virus via droplets and particles that can linger in the air for a few minutes to several hours.

“There is evidence that under certain conditions, people with COVID-19 appear to have infected others who were more than 2 meters away. These transmissions have taken place. in confined spaces that had inadequate ventilation. Sometimes the infected person would breathe heavily, for example while singing or exercising, ”the CDC explains. The infected were in the same space at the same time or shortly after the departure of the person with COVID-19.

What is the mechanism of infection?

“When people with COVID-19 cough, sneeze, sing, talk or breathe, they produce respiratory droplets. These droplets can vary in size from larger droplets (some of which are visible) to smaller droplets. Small droplets. can also form particles when they dry very quickly in the air stream. Infections mainly occur from exposure to these respiratory droplets when a person is physically close (within 2 meters) to a person with Covid-19 ” recalls the CDC.

The closed box experience

Already last May, a study published in the scientific journal Proceedings of the National Academy of Sciences (PNAS), claimed that Covid-19 could also be spread through the simple act of speaking.

To reach this conclusion, the American researchers had carried out an experiment: they had installed a volunteer person in a closed box and had asked him to repeat the phrase “Stay healthy” for 25 seconds. At the same time, an analysis laser ran through the box.

Verdict? The American researchers calculated that the person locked in the box projected approximately 2,600 droplets of saliva into the air per second: and these remained suspended in the box for 12 minutes. Taking into account the (known) concentration of the coronavirus in the saliva of an infected person, scientists therefore estimate that a person infected with Sars-Cov-2 could emit up to 1000 droplets carrying the virus per minute, nothing that speaking …

To avoid spreading the coronavirus, the mask is essential

“This direct visualization demonstrates that normal speech generates droplets in the air which can remain suspended for tens of minutes or more, and are eminently capable of transmitting disease in a confined space” conclude the authors of this work. Hence the (capital) importance of wearing a protective mask, in particular in confined spaces – public transport, shops, workplaces … and of adopting the new social distancing of 2 m between people.

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