US study: Corona droplets carry further than expected

Ontario – Standing the recommended distance away from people to avoid catching Covid-19 – the disease caused by the new coronavirus – may not be enough to protect you from someone who coughs in your direction.

A Canadian study found an unobstructed cough could travel two metres (six feet) in less than three seconds and keep going, well beyond the internationally accepted minimum distance that people are being asked to observe during the pandemic.

The study, led by Canada’s Western University and accepted for publication by the journal Indoor Air, was conducted well before the emergence of the current health crisis – up to the 2017-18 flu season – but has clear implications for the fight against Covid-19.

“Even when you are 2.5 metres away, the airflow in the cough can still be moving at 200mm [eight inches] a second,” said Eric Savory, professor from Western University’s department of mechanical and materials engineering. “The very fine droplets are going to remain suspended for a long time, even after four seconds.”

A separate American study on the new coronavirus has reinforced the argument in favour of that covering the mouth with a damp cloth curbs the emission of droplets during speech.

Research published by The New England Journal of Medicine found significant differences between the number of droplets produced, and their distance of travel, when a person spoke with their mouth covered and uncovered.

In the experiment, almost no droplets were observed when the participant said “stay healthy” while his mouth was covered with a slightly damp flannel. In contrast, he generated nearly 350 droplets when speaking at his loudest volume with his mouth uncovered.

The researchers, from the National Institutes of Health in Bethesda and Perelman School of Medicine at the University of Pennsylvania, also found the droplets travelled about 5-7.5cm (two to three inches) before they hit a light sheet. Speaking at a lower volume generated 230 droplets.

The number of droplets was highest on the “th” sound in the word “healthy”, the research showed.

“[The] video should convince you that, at a minimum, wearing a mask reduces dispersion of particles into environment,” tweeted Tom Frieden, former director of the Centres for Disease Control and Prevention and commissioner of the New York City Health Department.

“If done right, can’t hurt and might help,” he said.

The World Health Organisation has said the virus is primarily transmitted through respiratory droplets and contact routes. It can also be transmitted by direct contact with infected people and indirect contact with surfaces in the immediate environment or with objects used by the infected person.

“Whereas large droplets fall quickly to the ground, small droplets can dehydrate and linger as ‘droplet nuclei’ in the air, where they behave like an aerosol and thereby expand the spatial extent of emitted infectious particles,” the American researchers said. (SCMP)