Cough Chamber Shows Six Feet of Social Distancing May Not Be Enough to Prevent Spread of All COVID-19 Contact

Researchers conducting an experiment using a "cough chamber" have found that droplets filled with germs can travel for more than six feet after being expelled from the mouth of an infected person.

According to a team of researchers from Western University and Sunnybrook Hospital, the results suggest that the widely recommended six-foot physical distancing rule may be insufficient in cases when someone coughs directly at you without covering their mouth.

The Centers for Disease Control and Prevention (CDC) says that COVID-19 mainly spreads between people in close contact, or within about six feet.

When an infected individual coughs, sneezes or talks, droplets are launched out of their mouth or nose, and some of these may land in the mouths or noses of those nearby. The droplets can also be inhaled into the lungs.

The Western and Sunnybrook scientists conducted their latest research—which has been accepted for publication in the journal Indoor Air—during the 2017-2018 flu season, before the COVID-19 pandemic began. Nevertheless, they say the results may still applicable to the transmission of the novel coronavirus.

For their research, the team—led by Eric Savory from Western's Department of Mechanical and Materials Engineering—constructed a "cough chamber" to study the coughs of people who had naturally been infected with influenza.

The chamber is essentially a sealed wood and glass box with a hole at one end in which participants can safely cough into. A camera and a laser are fitted inside the box to work out the speed of the droplets expelled by the coughing individual.

"It is a two-meter cubic box with a small hole in the middle of one end. People rest their heads at the hole (a bit like when they have their eyes tested at an optometrist) so everyone is always at the same position. They then cough several times and for each cough we measure its speed at many places in a region one meter away from their mouth," Savory told Newsweek.

"We use it to study the coughs of sick people, the same people when they have recovered and a group of healthy people for comparison purposes," he said.

Savory and colleagues found that the droplets expelled will reach you within three seconds if you are standing six feet away from an individual who coughs unobstructed. Furthermore, these droplets will continue to travel beyond this distance, and some will still be floating in the air within the distance for up to three minutes after the cough.

"No-one has measured one meter from the mouth before and we have found that the peak airspeed of a cough at [this distance] is typically around one meter per second. We used the experimental data to build a computer model of an entire cough jet and we put droplets of different sizes into the cough, representing the measured droplet sizes in real coughs," Savory said.

"We found that even at 2.5 meters away from the mouth the peak airspeeds as the cough passes
are around 0.2 meters per second and about 10 percent of the droplets that were in the initial cough are still airborne in the cough," he said.

In addition the team found that sick and healthy people tend, on average, to cough with the same strength and so produce similar airspeeds with the droplets they expel.

The graphic below, provided by Statista, illustrates the number of confirmed COVID-19 cases as of April 15.

While the research was conducted on influenza patients before the current pandemic started, Savory says that the results would likely be similar if the experiment used people infected with COVID-19. In fact, he is now conducting further research to examine how COVID-19 droplets move through the air.

For Savory, the recommended six foot distancing rule is sufficient to prevent many COVID-19 infections, although being further away is clearly favorable.

"The two-meter distance represents a reasonable compromise to effectively mitigate the spread whilst allowing us to live our lives in a practical way. The evidence so far suggests that COVID-19, unlike some seasonal flus, is not transmitted very well at all over large distances in airborne droplets," he said.

"The main routes of infection seem to be more direct—people touching surfaces that have been contaminated by droplets or droplets directly depositing on the face from a cough or sneeze from someone else."