Airborne spread is real, say experts

The alarming message about the transmission of COVID-19 reached Twitter audiences on Sunday.

“The debate over whether the airborne transmission route occurs is over. Many of us have claimed its relevance from very early in this pandemic. it was real then. it is real now. period.”

The message was posted by dr. Richard L. Corsi, dean of engineering and computer science at portland State University, and one of 239 scientists appealing to the World Health Organization and other national health bodies to formally recognize the potential for the airborne spread of COVID-19.

In a commentary published Monday in the journal of Clinical Infectious Diseases, the international group of scientists warn there is every reason to expect that, like other coronaviruses, SARS-COV-2 can be spread via microscopic repository droplets small enough to remain aloft in the air and capable of travelling the space of a room.

Most public health bodies, including the WHO, don’t recognize airborne transmission of COVID-19, except for certain aerosol-generating medical procedures. Instead, the messaging is that COVID-19 is spread primarily by close contact and larger respiratory droplets spewed out when people sneeze or cough, and that these liquid droplets typically spread only one or two metres before dropping to the ground.

However, as the Post’s Tom Blackwell reported in April on evidence air conditioning is helping COVID19’S spread, scientists have argued that as droplets from an infected person start to evaporate, the resulting smaller particles can indeed become airborne.

“Hand-washing and social-distancing are appropriate, but in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people,” the scientists wrote in Clinical Infectious Diseases.

The problem is a matter of “heightened significance now, when countries are reopening following lockdowns — bringing people back to workplaces and students back to schools, colleges and universities,” they said.

Airborne transmission of COVID-19 is not only a “real risk,” they added. It seems the only plausible explanation for several superspreading events, including an outbreak at a restaurant in the

Chinese city of Guangzhou involving 10 people.

“All routes of transmission must be interrupted” until vaccines become available, they said. Measures to slow airborne transmission include sufficient and effective ventilation (more clean outdoor air, less recirculating air) in public buildings, workplaces, schools, hospitals and nursing homes; airborne infection controls like germicidal UV lights; and avoiding overcrowding, especially in public transport and public buildings.

“Simple things can make a big difference,” tweeted co-author Donald Milton, a professor of environmental health at the University of Maryland. “Wear masks whenever you are not at home, even simple homemade masks can have a major impact. Open windows. Don’t gather in large groups inside with singing and loud talking.”

Several public health officials have been quick to dismiss the possibility of airborne transmission, “which does not strike me as being very cautious when you are dealing with a virus which is still new and is causing a very severe pandemic,” said Dr. Raymond Tellier, a medical microbiologist at Mcgill University Health Centre who contributed to the commentary.

Under the precautionary principle, “you don’t have to await scientific certainty to take extra precautions.”

Why the reluctance from officials? “It’s very inconvenient to acknowledge aerosol transmission because it takes a lot more work to deal with it,” Tellier said. “Certainly not everyone who has worked with COVID patients has been infected. But there have been a very high number of health-care workers worldwide that have been. This is something that needs to be re-examined very carefully.”

It’s not clear what dosage or amount of small airborne virus particles would need to be inhaled for someone to become infected. “We do not know that for COVID,” Tellier said.

But studies by the signatories and other scientists have demonstrated — “beyond any reasonable doubt” — that tiny, virus-laden aerosolized droplets released when people exhale, talk and cough can float in the air and drift long distances on currents, potentially tens of metres, they wrote.

When reached for comment, the Public Health Agency of Canada said it couldn’t immediately respond to the National Post’s questions on airborne transmission. The agency said it has sent the request to experts, and would provide a response this week.

The agency’s website says human coronaviruses are most commonly spread through respiratory droplets, close, prolonged personal contact, and touching an infected surface or object then touching mouth, nose or eyes.

According to the B.C. Centre for Disease Control, “currently health experts believe that coronavirus cannot be transmitted through airborne transmission.”

The WHO is also reviewing the commentary with its technical experts.

It’s hard to unravel which transmission route — droplets via close contact? airborne? contaminated hands? — is most important, because it depends on the setting, said Tellier. “In poorly ventilated settings you would expect aerosol transmission to increase.” The same is likely true for choir singing, he said.

Breathing and speaking also emit small-sized aerosols, which might answer why asymptomatic people who aren’t coughing or sneezing can transmit the virus.

Wearing masks is “something that vigorously should be encouraged, absolutely,” Tellier said.

So should physical distancing, washing hands and isolating at home if someone has COVID symptoms, Corsi tweeted.

“And limiting, putting on pause, or modifying activities that generate the release of a lot of respiratory particles is just smart. Quieter = safer.”