Talking is worse than coughing for spreading COVID-19 indoors

Talking may lead to more transmission of COVID-19 than coughing does, particularly in poorly ventilated spaces, a new study finds. 

What's more, the study researchers found that under these conditions, the virus can spread more than 6 feet (2 meters) in just seconds.

The findings show that social distancing alone isn't enough to prevent COVID-19 transmission — face masks and adequate ventilation are also of vital importance to curb the spread, the authors said.

In October 2020, the Centers for Disease Control and Prevention (CDC) officially acknowledged that SARS-CoV-2, the virus that causes COVID-19, can spread via "airborne transmission," or small droplet particles that linger in the air, particularly in enclosed spaces with poor ventilation, Live Science previously reported.

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In the new study, published Tuesday (Jan. 19) in the journal Proceedings of the Royal Society A, the researchers used a mathematical model to examine how COVID-19 spreads indoors depending on the size of the space, the number of people inside, how well the space is ventilated and whether people are wearing face masks.

The study found that when two people are in a poorly ventilated space and not wearing masks, prolonged talking is much more likely than a short cough to spread the virus. That's because when we speak, we generate small droplets that can hang in the air, spread and accumulate in an area without adequate ventilation. On the other hand, a cough produces more large droplets, which quickly fall to the floor and settle on surfaces.

In one modeled scenario, the researchers found that after a short cough, the number of infectious particles in the air would quickly fall after 1 to 7 minutes; in contrast, after speaking for 30 seconds, only after 30 minutes would the number of infectious particles fall to similar levels; and a high number of particles were still suspended after one hour. In other words, a dose of virus particles capable of causing an infection would linger in the air much longer after speech than a cough. (In this modeled scenario, the same number of droplets were admitted during a 0.5-second cough as during the course of 30 seconds of speech.)

However, wearing masks of any kind reduces the amount of airborne coronavirus because the masks filter some of the droplets and slow the momentum of exhaled particles, the author said in a statement.

Ventilation also matters — one of the modeled scenarios found that when an infected person spoke indoors for one hour, others in the room faced up to a 20% risk of infection, but this risk was reduced by a factor of three when the air in the room was completely changed 10 times per hour. (In a well-ventilated room, there are typically 10 to 20 air changes per hour.) 

"Ventilation … is of utmost importance in minimizing infection risk indoors," the authors, from the University of Cambridge and Imperial College London, both in the United Kingdom, wrote in their paper. 

"Our knowledge of airborne transmission of SARS-CoV-2 has evolved at an incredible pace, when you consider that it's been just a year since the virus was identified," study lead author Pedro de Oliveira of Cambridge's Department of Engineering, said in a statement. "We show how these small droplets can accumulate in indoor spaces in the long-term, and how this can be mitigated with adequate ventilation."

The researchers have used their findings to create a free online tool, called Airborne.cam, to show how ventilation and other factors affect the risk of transmission indoors. The tool could be used by people managing workplaces and classrooms to help determine if ventilation is adequate, the authors said.

Originally published on Live Science.