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Coronavirus: Do droplet-spreading runners need to stay far away from other pedestrians?

Last Updated Jul 14, 2020 at 9:49 pm PDT

FILE (iStock)

Computer simulation showed potential for exercisers to spread virus far, but other study suggests lower risk

Dr. Bonnie Henry: Risk of passing runner spreading COVID-19 'infinitesimally small'

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In early April, a series of animated computer simulations purportedly showing how runners and cyclists can spread the coronavirus to those they pass outdoors went viral online.

The animations came from Belgian engineers, who simulated the spread of exhaled droplets, represented as colourful dots spreading rapidly around – and potentially infecting – other pedestrians.

The research spurred news stories around the world, with many readers interpreting it as evidence that running and cycling posed a grave threat to them.

But the researchers were also criticized for publicizing their results before being published in a peer-reviewed journal – or even publishing a pre-print (not peer reviewed) study.

Lead researcher Bert Blocken, a professor of civil engineering at Eindhoven University of Technology, defended his unusual communication strategy on Twitter, saying the COVID-19 “crisis is urgent.”

“So exceptionally we turned order upside down: (1) media, (2) today I submitted the proposal for funding (3) peer review article later.”

Blocken released a pre-print of the study in mid-April, examining the spread of airborne droplets, concluding that the slipstream behind a runner or cyclist could spread the coronavirus – with people following directly behind an infected exerciser at the greatest risk.

“The results indicate that the largest exposure of the trailing person to droplets of the leading person for walking and running is obtained when this trailing person is in line behind the leading person, i.e. positioned in the slipstream,” the study says.

The study suggested people stay 10 metres behind a runner or slow biker and 20 metres behind someone biking quickly.

But other research suggests the risk of contracting COVID-19 is much lower outdoors than it is indoors.

Chinese researchers found only one outbreak out of 318 analyzed could be linked to “an outdoor environment.”

“All identified outbreaks of three or more cases occurred in an indoor environment, which confirms that sharing indoor space is a major SARS-CoV-2 [novel coronavirus] infection risk,” the pre-print study concludes.

In late April, B.C.’s provincial health officer, Dr. Bonnie Henry, said the evidence the risk of a passerby spreading the coronavirus to someone else outdoors is “infinitesimally small.”

“The risk that someone who is sick is spreading this virus from coughing or sneezing outside, and you walk by them very quickly, even if it is within six feet, that risk is negligible. That is not the way this virus is mostly transmitted,” she said.

But Henry encouraged outdoor enthusiasts to give others plenty of space while outdoors, even if it’s just to give others peace of mind.

“Right now we need to be very cautious, we need to be kind with each other, we need to recognize that we still have a lot of anxiety and people are very concerned about this,” she said.

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