Tag Archives: droplets

Heavier breathing, spewing droplets, poor ventilation add to gyms’ superspreading risk

A recent COVID-19 outbreak at a southern Ontario fitness studio is illustrating how certain indoor settings can provide a perfect storm for superspreading events.

The studio, a downtown Hamilton Spinco location, has been connected to 69 cases of COVID-19 as of Wednesday, despite screening customers, operating at 50 per cent capacity and keeping the recommended two-metre radius around bikes.

So how did so many cases originate there? And does it raise concern about how the novel coronavirus can spread in a gym setting?

“Certainly, this event makes you wonder that,” said Dr. Matthew Oughton, an infectious disease expert at Jewish General Hospital and McGill University in Montreal.

“I can see where this could lead to perhaps gyms having serious restrictions placed on them if they want to avoid similar superspreading events.”

Ontario and Quebec recently reintroduced closures at gyms in virus hot spots, including Toronto, Montreal and Ottawa, for a four-week period to help limit spread.

And Dr. Barbara Yaffe, Ontario’s associate chief medical officer, said Wednesday authorities are reviewing guidelines for fitness studios across the province after the Hamilton outbreak.

Oughton said gyms and fitness studios have a few strikes against them when it comes to tailoring them for the pandemic.

Heavier breathing expels droplets farther

They’re operating almost exclusively indoors, which makes for poorer ventilation, and patrons aren’t usually masked when engaging in strenuous exercise.

High-impact activity also leads to heavier breathing, which means droplets are being expelled from peoples’ mouths at an accelerated rate — and being propelled farther distances.


An employee at a Gatineau, Que., gym wipes down equipment in late June during the pandemic. When people are exercising vigorously, the volume and distance of what comes out of their mouth and their lungs differs than when they speak normally. (Frédéric Pepin/Radio-Canada)

Dr. Andrew Morris, a professor of medicine at the University of Toronto, likens it to throwing a ball. The harder you throw, the farther it goes.

“We still don’t have a perfect understanding of this,” he said. “But we do know that when people are exercising vigorously, the volume and distance of what comes out of their mouth and their lungs is dramatically different than when somebody is speaking [in a normal way].”

WATCH | Dr. Theresa Tam, Canada’s top doctor, on aerosol transmission:

Chief Public Health Officer Dr. Theresa Tam admits that guidance regarding the transmission of COVID-19 may have to change. 1:00

If people are shouting, cheering or singing — which often happens in a spin class where music is blaring and instructors spew out encouragement to keep participants’ intensity up — that can make things worse.

“And if you mix that in with a space that may not have proper ventilation, there is risk for a lot of spread to occur,” Morris said.

Dr. Ilan Schwartz, an infectious disease expert with the University of Alberta, said spin classes may pose more risk than other group settings because of the bikes themselves. In theory, the rapidly spinning wheels could aerosolize droplets by flinging them farther distances.

“I haven’t seen any studies of this, but theoretically it makes sense,” he said.

“I think going to the gym isn’t necessarily high-risk, unless individuals are close together and there’s poor ventilation. But there might be specific circumstances that could make it higher-risk, where something with fast, moving parts [or] a rapidly moving fan can generate aerosols as well.”


Holland Philpott participates in an outdoor yoga class in a dome to facilitate distancing and proper protocols to prevent the spread of COVID-19, in Toronto in June. (Carlos Osorio/Reuters)

But Morris said the real danger comes when people are spewing out droplets in a poorly ventilated space.

Fitness class dangers not equal

The prolonged length of time spent in a spin class, typically one hour, and the number of people in the room will also impact risk.

Not all fitness classes will present the same dangers, he added.

A low-impact yoga class where hearts aren’t racing and breathing is kept under control seems safer than a high-impact spin class but not if it’s crowded and poorly ventilated.

A dance class, where participants are crisscrossing into airspace previously occupied by others, can be risky as well in the same environment.


A lone jogger, wearing a protective face mask, runs with her dog in the Tuileries Garden in Paris as a lockdown is imposed in March. Masks, while uncomfortable when working out, can be worn. (Charles Platiau/Reuters)

“Assuming that room has relatively poor ventilation, that’s the kind of setting where yes, you’d be concerned about the potential for transmission,” Oughton said. “But if you had the exact same room with an excellent HVAC system, or the same room where windows were kept open … those are the kinds of things you could do to reduce the risk.”

Morris said finding ways to make these activities safer is always better than banning them.

Masks, while uncomfortable when working out, can be worn in most instances, he said. Improving ventilation and limiting numbers of people even further can also help.

“If we’re going to be successful, we can’t keep telling people they can’t have these things,” Morris said. “We need to be able to point to something and say, ‘This is the better choice.”‘

Schwartz said frequent hand-cleaning and the sanitization of equipment should also be kept in mind, even if surface transmission isn’t as concerning as it was earlier in the pandemic.

“And for now, I think it’s probably a good idea to avoid spin classes,” he added.

Oughton foresees people taking their workouts outdoors in new ways over the winter if gyms and fitness centres are deemed too risky.

That could mean dusting off the skates or ski boots.

“I think this is going to re-emphasize the safety and the necessity of being able to get some activity and fresh air outside,” he said.

“Hopefully, we find new appreciation for outdoor winter sports that we can all enjoy.”

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Scientists try to ‘see’ invisible transmission of coronavirus through respiratory droplets

This is an excerpt from Second Opinion, a weekly roundup of eclectic and under-the-radar health and medical science news emailed to subscribers every Saturday morning. If you haven’t subscribed yet, you can do that by clicking here.


The coronavirus that causes COVID-19 spreads through droplets that we spew as we breathe, talk, cough and sneeze — so tiny that they’re invisible to the naked eye. 

That’s why questions remain about the virus’s transmission and what precautions need to be taken to curb its spread as governments begin to lift restrictions. Will it help if everyone wears a mask? Is keeping everyone two metres apart far enough?

Some researchers aim to learn more about transmission by trying to make invisible sneezes, coughs and breaths more visible. Here’s a closer look at that research and what it might reveal.

How do scientists think COVID-19 is transmitted?

According to the World Health Organization, the disease spreads primarily through tiny droplets expelled when a person infected with SARS-CoV-2 sneezes, coughs, exhales or spits while talking. They can infect another person who:

  • Comes into contact with those droplets through their eyes, nose or mouth (droplet transmission).

  • Touches objects or surfaces on which droplets have landed and then touches their eyes, nose or mouth (contact transmission).

The WHO says it’s important to stay “more than one metre away” from a person who is sick. But the Public Health Agency of Canada recommends staying a distance of at least two metres or two arms’ lengths away, not just from people who are sick but from all people you don’t live with.

Why is 2 metres the recommended distance for preventing transmission?

Scientists in the 19th century showed respiratory droplets from a person’s nose and mouth can carry micro-organisms such as bacteria and viruses.

Then, in 1934, W.F. Wells at the Harvard School of Public Health showed that large droplets (bigger than 0.1 millimetre) tended to fall and settle on the ground within a distance of two metres, while smaller droplets evaporated and the virus particles left behind could remain suspended in the air for a long time.


Wells proposed that could explain how diseases are transmitted.

Since then, respiratory diseases have been divided into those transmitted via droplets (usually from close contact) and those that are airborne and can spread over longer distances, such as measles or tuberculosis. 

Such tiny particles are presumably pushed around by air currents, but can’t move easily due to air resistance. So their actual movements haven’t been well modelled or measured, said Lydia Bourouiba, professor and director of the Fluid Dynamics of Disease Transmission Laboratory at the Massachusetts Institute of Technology. 

“And that’s why the notion of airborne [transmission] is very murky,” said Bourouiba, who is Canadian.

Why don’t experts think the virus is airborne?

A pair of recent studies raised the notion of airborne transmission, but Mark Loeb, a professor at Hamilton’s McMaster University who specializes in infectious disease research, cautions against putting too much stock in them. 

Researchers found traces of RNA from SARS-CoV-2 in washrooms and some high-traffic areas in hospitals in Wuhan, China, and in Nebraska, and suggested it got into those areas through the air, though there was no evidence the particles were still infectious. 


Government guidelines in Canada recommend that people stay at least two metres away from others as part of physical distancing measures to curb the spread of COVID-19. (Gary Moore/CBC)

Loeb said that’s just a “signal” that part of the virus was there. 

“Does it mean that COVID-19 is spreading from person to person through aerosols? I would say definitively not,” Loeb said. 

If the virus were airborne, we’d know by now, said Dr. Allison McGeer, because every health care worker would be infected despite wearing personal protective equipment.

“You and I don’t have to worry walking down the street that we’re going to be breathing the air of somebody who walked down the street five minutes ahead of us who had COVID-19 and didn’t know it,” said McGeer, an infectious disease specialist with Sinai Health in Toronto who is leading a national research team studying how COVID-19 is transmitted. “That we can be confident about.”

Is there evidence the virus could be spread farther than 2 metres?

Some studies, including Bourouiba’s, show that droplets from coughs and sneezes can, in fact, travel much farther than expected. Bourouiba’s high-speed imaging measurements and modelling show smaller respiratory droplets don’t behave like individual droplets but are in a turbulent gas cloud trapping them and carrying them forward within it. The moist environment reduces evaporation, allowing droplets of many sizes to survive much longer and travel much farther than two metres — up to seven or eight metres, in the case of a sneeze

WATCH | Close-up view of the droplets released by a person sneezing

(Credit Lydia Bourouiba/MIT/JAMA Networks)

She said the research “is about revealing what you cannot see with the naked eye.”

A more recent Canadian study used a “cough chamber” to show that if someone coughs without covering their mouth, droplets from the cough are still travelling at a speed of about one kilometre per hour when they hit the two-metre edge of the chamber. Within the chamber, droplets remained suspended for up to three minutes. 

WATCH | The speed and distance travelled by droplets from a cough

Dr. Samira Mubareka, a virologist at Sunnybrook Hospital in Toronto who co-authored the study, said it “gives you a sense of what the possibilities are,” but noted that the researchers, who were studying flu patients, detected very little virus in the droplets.

What does that say about the 2-metre guideline?

Bourouiba says her research points to the potential for exposure beyond two metres from someone who is coughing and sneezing. As she wrote in the journal JAMA Insights in March, that means it’s “vitally important” for health care workers to wear high-grade personal protective equipment in the form of respirators even if they’re farther than two metres away from infected patients.  

However, she does think two metres can be far enough for healthy people in the general public in most environments, since breathing and talking don’t propel droplets and surrounding cloud too far.

Mubareka stands by the two-metre guideline despite the findings of her cough chamber study.

Because despite dramatic images of respiratory droplets being propelled from someone’s nose and mouth, it’s not yet clear how many of them contain virus and how many are infectious.

“And that’s really the key variable — that’s what really determines your risk,” she said. “Those are the kinds of things we haven’t been able to measure.” That may change, she added, with the recent invention of particle samplers designed specifically for viruses.

Loeb of McMaster, notes that a cough chamber and similar laboratory setups are highly artificial settings and controlled environments.

“They’re basically saying what’s theoretically possible,” he said. “I think those are provocative and those are hypothesis- generating, but then they need to be tested in the field.”

Loeb is running such a field test himself — a randomized controlled trial of the use of medical versus N95 masks among health care workers to see if there is a difference in the transmission of COVID-19.

But are coughing and sneezing all we need to worry about?

That’s a question on a lot of people’s minds, given that a growing number of studies have shown asymptomatic and pre-symptomatic transmission is possible, especially among those who live with an infected person. 

Even though researchers aren’t sure exactly how people without symptoms transmit the disease, the new evidence has prompted both U.S. and Canadian officials to suggest apparently healthy people wear masks in public to protect others — “because it prevents you from breathing or speaking moistly on them,” Prime Minister Justin Trudeau famously explained.

“People generate particles when they’re talking, singing, breathing — so you don’t have to necessarily be coughing,” Mubareka said. “It’s just that maybe the dispersion is a little bit more limited.” 

WATCH | The droplets produced when someone speaks with, and without, a mask

This video, from a study published in April 2020 the New England Journal of Medicine by researchers at the U.S. National Institutes of Health, uses laser light scattering to show droplets produced when someone speaks. 0:42 

A recent brief video and report by U.S. National Institutes of Health researchers used lasers to show that droplets projected less than 10 centimetres when someone says the phrase “Stay healthy.” It found the louder someone spoke, the more droplets were emitted.

But they were dramatically reduced if a damp washcloth — a stand-in for a mask — was placed over the speaker’s mouth.

So what about using masks to curb the spread of COVID-19?

Studies have already provided evidence that the rate at which sick people shed the virus into their surroundings is reduced when they wear a mask. 

Other studies, such as a 2009 paper in Journal of the Royal Society Interface, use imaging to show how wearing a mask while coughing reduces the jet of air that’s normally directed forward and down. A surgical mask “effectively blocks the forward momentum of the cough jet and its aerosol content,” the study found. Some does leak out the sides, top and bottom, but without much momentum.


A 2009 study by researchers in the U.S. and Singapore uses schlieren imaging to show airflow from a person’s mouth a) without a mask b) with a medical mask and c) with an N95 mask. (Gary S. Settles/Penn State University/Journal of the Royal Society Interface)

The World Health Organization recommends that people wear masks if they are coughing and sneezing or if they are caring for someone who is sick.

It notes that studies haven’t been conducted yet on whether or not transmission is reduced when healthy people wear masks in public, but it encourages countries to look into that. 

Many governments haven’t waited. Los Angeles, Italy and Austria are among the places that have begun requiring customers to wear masks while shopping


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