The COVID Danger of the Cough Stream

"The key findings are that, on average -- and this is over many, many different coughs, because there are weak coughs and strong coughs -- the air is still moving at about one metre a second, a metre away from the person, which is not insignificant."
"And certainly it's difficult to get away from someone who coughs at you if it's moving at a metre per second, and you're a metre away from them."
"We also coupled this with some computer modelling to then extrapolate further distances with some confidence. That's how we're able to say that two metres away you've still got significant velocity. Two-and-a-half metres away it still could be moving at 200 millimetres a second."
"The advice that everyone has been given, which is you should stay two metres away is very sound, in that it's a practical distance. Clearly the further away you are -- three metres, four metres --the better."
"But two metres is certainly better than one metre, which is certainly better than being close to somebody."
Eric Savory, department of mechanical and material engineering, Western University

A new study out of Western University suggests germs from coughing are propelled much farther than the two-metre physical distancing rule recommended by doctors suggests. (Shutterstock)

Scientists at Western University in London, Ontario undertook an experiment with seasonal influenza to determine a measure of safe distance from someone with the virus who coughs, potentially transmitting viral drops to anyone in the near vicinity. Although the experiment focused on the flu and its likelihood of distance-infection, its findings also have applications for the novel coronavirus and the generalized warning to remain a distance of two metres (six feet) away from others in case they may be infectious, without the classical symptoms.

In league with virologist Samira Mubareka of Sunnybrook Hospital in Toronto, the Western University researchers set out to recruit people from the Western campus who had been referred and who had typical flu-like symptoms. These were ill people in their 20s, but who agreed to come to the laboratory -- also on campus -- to take part in the proposed study. The purpose of which was to measure how far and swiftly particles of influenza propel through the air in a cough jet. What the scientists determined was that within three seconds viral droplets can reach another person and will "continue to projectile forward well beyond the recommended six feet (distance)".

The 'cough chamber' at Western University measures how far germs are propelled from someone's airways when they cough and how long the droplets carrying germs stay in the air. (Western University)

The coughs of the ill volunteers were measured and sampled initially. They then returned after a month had elapsed to undergo identical measurements once again. Following which a group of healthy people also recruited across campus in the age range of 18 to 30 had their coughs measured as well, to determine differences that might exist between coughs and the distance they travel. They did this with the use of a 'cough box', an enclosure two-metres tall and wide where volunteers rest their chin on a device, and then cough.

The scientists tracked the movement of each cough airflow, introducing fine micron-sized solid particles into the flow, then examined the particle displacement, and taking the measure of velocity vectors, magnitude of the velocity at about a metre away. They found that very fine droplets remain airborne for longer than the recommended six feet (two metres) distance. Eventually they become dispersed.

One perplexing question remains; virologists are unable to judge with any degree of exactitude what dosage is required to be inhaled before infection occurs. Although many fine droplets can be inhaled containing virus droplets, the dosage sufficient for infection to take place remains unknown.

When the pandemic began, protective shields like this one started popping up to protect cashiers from the transmission of germs. (Pierre-Olivier Bernatchez /CBC)