COVID-19 likely spread by building ventilation
Canadian researchers working on an HVAC fix
The outbreak of COVID-19 at a restaurant in the southern Chinese city of Guangzhou was a puzzle.
The suspected index patient was a visitor from the coronavirus’s epicentre in Wuhan. But the eight other customers who later tested positive were not sitting close enough for droplet transmission, and most of the patrons and staff avoided infection altogether.
A team of local scientists eventually came to an eyeopening conclusion about the episode: tiny particles of virus had hitched a ride on currents created by the eatery’s airconditioning.
For a group of civil engineers at the University of Alberta, the finding was no surprise. In their world, they say, it’s well known that building ventilation systems are efficient discriminators of virus and other pathogens and believe the COVID-19 bug is no exception.
Aided by a $440,000 federalgovernment grant, they’re now working on ways that buildings could change their HVAC setups to curb the risk of infection, what the researchers call a “non-pharmaceutical” intervention against the disease.
“We want to save lives, let’s cut right to the chase,” said Prof. Brian Fleck, part of the project. “There are so many, many, many buildings … This affects absolutely everybody. Billions of people. If we are able to cut down the transmission rate by a per cent, that’s a lot of people.”
The engineers’ belief in the importance of building ventilation as a transmitter of the COVID-19 virus is not universally held.
The World Health Organization and other public-health bodies, citing the science to date, say the pathogen is spread almost entirely by droplets, heavier particles emitted mostly when infected people cough or sneeze, and which fall down within a short distance. Hence the two-metre rule for social distancing.
“The HVAC systems in most non-medical buildings play only a small role in infectious disease transmission, including COVID-19,” argued the American Society of Heating, Refrigerating, and Air-conditioning Engineers last month.
But Chinese and Australian air-quality experts, citing in part the experience with SARS, another coronavirus, argued in a paper earlier this month that as droplets from an infected person start to evaporate, the resulting smaller particles can indeed become airborne.
INFECTED VIA AIR DUCTS
They point to evidence that passengers confined to their cabins on cruise ships like the Diamond Princess were infected through the vessels’ air ducts.
“It is highly likely that the SARS-COV-2 virus also spreads by air,” they conclude, urging “all possible” action in response, including modifications to ventilation systems. “We predict that … failure to immediately recognize and acknowledge the importance of airborne transmission and to take adequate actions against it will result in additional cases.”
Then there was the Guangzhou restaurant case, detailed in a U.S. Centers for Disease Control online journal recently. Researchers concluded flow from an air conditioner moved over three tables, carrying virus from the infected patron at the middle one to the far table, then back to the diners closest to the air conditioner.
Heating, ventilation and air conditioning (HVAC) engineers have long known that tiny particles of pathogen can be carried in the air that is circulated, heated and cooled in modern buildings, said Fleck. He pointed to Legionnaires disease, a bacterial pneumonia first traced to a hotel’s airconditioning system.
“This has been on people’s radar for quite a while,” he said. “Somebody on a different floor sneezes … The particle can stay airborne long enough to go all the way through the system and then pop out in somebody else’s office.”
There are various ways that risk can be lessened, including use of filters that catch a greater number of those particles, and drawing more fresh air into a system. It also is likely that higher levels of humidity — a factor that only some Canadian buildings can adjust — will help kill off the virus, said Fleck.
But each of those changes carries a cost. Adding more fresh air can require additional heat or air conditioning. Heavier filters means more energy is needed to push the air through them. And more humidity can lead to mould, he noted.
“This will make for difficult decision-making.”
Funded by the Canadian Institute for Health Research, the University of Alberta project is led by engineering professor Lexuan Zhong and also involves pediatrics professor Lisa Hartling. It consists of three phases: systematically reviewing literature on air circulation and viruses, determining what strategies would be effective and then carrying out a detailed audit of all the buildings on the Edmonton campus to create a real-world model of what should be done.
The team hopes to have solid results by the summer of 2021, said Fleck.