Hundreds of scientists are sounding the alarm over the possibility that the novel coronavirus may spread through the air more than we once thought.
On Saturday, the New York Times reported that 239 scientists will warn the World Health Organization that the virus can linger in the air and infect those nearby. The researchers plan to publish their evidence in a journal next week.
But some Canadian infectious disease experts stop short of it being a critical cause for concern just yet.
While there’s value in looking more closely at the risk associated with smaller, aerosol particles carrying the virus, the main point of transmission will still be the larger droplets, said Colin Furness, an infection control epidemiologist and assistant professor at the University of Toronto.
“Being ‘airborne’ is a big scary word… but most people don’t spend their time cooped up with people who have COVID,” he said.
“What these scientists are saying here is that we haven’t paid enough attention to the smaller droplets. Smaller droplets might also be dangerous. There are little aerosol droplets with the virus in them, but we haven’t been able to culture that. We don’t know that they’re actually infective or by how much.”
The World Health Organization has said the virus mainly spreads by droplets, hence the emphasis on physical distancing, hand-washing and shuttered public spaces.
Droplet transmission happens when an infected person coughs, sneezes or speaks. This generates a variety of droplet sizes. The focus has so far been on the larger droplets as the main source of transmission.
However, the group of scientists is warning that much smaller droplets may suspend or glide the length of a room and infect people when inhaled. They’re calling for the WHO to consider the risk and revise its recommendations.
While most scientists agree big droplets are the culprit behind the majority of infections, part of the issue is that the evidence isn’t solid on either side, said Dr. Michael Gardam, an infection-control expert and chief of staff at Toronto’s Humber River Hospital.
It’s been a long-standing debate, one that Gardam says has been discussed since the SARS outbreak in 2003.
“This whole movement started up saying, you know, there are these tiny, tiny particles that can get on into the air currents and can flow far beyond the sort of two metres that we’re talking about here. And that day could be a potential mode of spread of these viruses.”
Gardam said while there is probably “some” airborne transmission “under certain circumstances,” he doesn’t think this is the main way in which this novel coronavirus is spreading.
“By and large, I believe, and I think many others believe, it’s probably not the predominant way that this is being spread,” he said.
But he said if the virus is, in fact, spreading through airborne transmission, it is going to require “unbelievable changes to the way the world is currently operating.”
What does this mean for Canadians?
Should airborne transmission become a more serious concern, hospitals would be the first to make changes, experts agree.
At this point, health-care workers in hospitals are not using N95 masks as they care for COVID-19 patients because basic surgical masks are effective enough to filter out the large droplets. The only caveat is when doctors perform aerosol-generating medical procedures, which whip up multiple smaller droplets.
But “it’s a simplification to say it’s airborne. It simplifies the problem,” said Alon Vaisman, infection control and infectious diseases physician at Toronto’s University Health Network.
“Our tools are very blunt. We don’t have anything in between a procedure mask or an N95 respirator. There’s this dichotomy that’s been created in the world of infection control. But to be precise, it’s more complicated than that.”
Hospitals might also tweak their air circulation systems, Vaisman said, making sure the air isn’t recirculated and instead pushed outside of the building.
Some Canadian researchers are investigating the possibility of the virus spreading through ventilation systems. Vaisman said the same changes to circulation could be implemented in places other than hospitals, but that it might not be totally necessary.
“This is not a primarily airborne virus,” he said. “We haven’t seen massive outbreaks in health-care facilities. We don’t see tons of doctors or nurses being sick and dying as a result of COVID, despite them all predominately wearing masks while providing face-to-face care for these patients.”
Increased use of UV light may also come into play in some settings, Furness added.
“The ultraviolet light essentially rips up the genetic material. It will deactivate the virus quite readily,” he said.
But, outside of places with known COVID-19 cases, few things would need to change, he continued.
“Almost everything we’re doing is still completely adequate. Everything you’re doing in your daily life still applies,” Furness said.
“It’s not great news for anyone who wants to imagine large crowds in small spaces. It makes that more worrisome. … Nightclubs, for example, if we thought they were a bad idea to reopen, now they’re a really bad idea.”
Some cases exist
There are several studies that suggest airborne transmission of the virus, while uncommon, has occurred.
Chinese researchers believe an outbreak at a restaurant in Guangzhou was linked to the building’s air conditioning system. They suspect an asymptomatic woman dined at the restaurant, later causing four of her family members and five others to fall ill.
According to the research, published in the journal of Emerging Infectious Diseases in April, the families were all seated farther apart than one metre. Droplets don’t commonly travel more than a metre or two, leading them to believe the air conditioning pushed the particles further.
A separate study published in the Proceedings of the National Academy of Sciences on June 11 argued that airborne transmission is the primary way the virus spreads. The researchers emphasized that a true understanding of how the virus spreads remains “uncertain,” but suggest airborne spread is “highly virulent and dominant.”
A ventilation system malfunction is also considered a factor in a coronavirus outbreak at a seniors residence in Quebec. The air quality concerns have prompted works and members of the Canadian Forces deployed there to wear N95 masks.
But these studies aren’t definitive of the virus’ behaviour, Furness said, and there’s still much unknown.
“The viral dose also matters,” he said. “How many does it take to make you sick? Well, no one knows. Big droplets have lots of virus. If you inhale that, that’s a big dose. These teeny tiny particles floating around, that’s a small dose. So now we need to figure out how much of a viral dose you need.”
It’s also not a “radically new way” for viruses to spread through tiny particles in the air, Furness said, pointing to others like the measles. However, it’s not a reason to panic, he said.
“It may mean we need to pay more attention to ventilation. We may need to pay more attention to COVID patients when we’re actually in the room with them,” he said. “And that’s really about it.”
— with files from Global News’ Katie Dangerfield and the Associated PressView link »