WHO has issued new advice after it can’t rule out airborne spread of COVID.
WHO acknowledges the possibility that outbreaks in restaurants, choirs and fitness centres around the world were the result of some aerosol transmission.
Guy Marks, an epidemiologist and respiratory physician at the University of New South Wales says, Given the likelihood of transmission at home, we need to think about the air exchange in the rooms where we spend most of our time. Remember, the average adult takes between 12 to 20 breaths per minute, so it doesn’t take long to real get a kind of “aerosol cloud” going.
“If people in a room and it’s all sealed, the air won’t change, it just sits there so anything you emit from breathing, coughing, whatever, just stays in the air,” Professor Marks says.
Air conditioning can be a good way to mechanically ventilate a space if you can’t open windows or doors. But there is one condition — it should not be used on the recirculate setting. “Otherwise there’s the potential that those aerosols will just keep being dispersed through the air-conditioner over and over,” Professor Marks said.
But while air conditioners are good for ventilation, they introduce another problem: direct air flow. If multiple people are sitting under an air-conditioner and one has COVID-19, the direct flow of air from the unit can create a loop of infected aerosols over everyone.
The three families were sitting within the blue cloud of aerosols.(Supplied: MedRxiv)
This diagram shows the mini weather-system created by an air-conditioner at a restaurant in China where a COVID-19 outbreak was recorded.The three families were sitting within the blue cloud of aerosols.(Supplied: MedRxiv). Research yet to be peer-reviewed, concluded a “recirculation envelope” formed over three families’ tables, which were in the direct line of one air conditioning unit. Ten members of those families later tested positive to COVID-19, but no-one else in the restaurant (who sat under different air conditioning units) was infected.
“It wasn’t caused by the air conditioner, it was just the fact it was a very directional flow,” Professor Morawska says.
Deciphering the direction and rebounding of air from a unit is hard, even for experts, so the best idea is just don’t sit in the direct path of a unit. “First thing when you enter a restaurant, look at where the air conditioner is and which way will the air go and which tables will be most affected,” Professor Morawska says. Also keep in mind, fans don’t help with ventilation as while they move air around, they don’t remove it.
“In these events, short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out,” the statement said.
On June 24th, the air cooling system used in a German slaughterhouse helped spread the coronavirus among hundreds of workers, a hygiene expert said on Wednesday, a day after the mass outbreak triggered renewed lockdowns in the area.
More than 1,500 out of 7,000 employees have tested positive so far at the Tonnies meat processing plant in the western district of Guetersloh in the country’s single biggest COVID-19 cluster to date. Professor Martin Exner, a hygiene expert at the University of Bonn tasked by Guetersloh district to study the outbreak, told a press conference that the plant’s air filtration system had contributed to the spread of virus-laden aerosol droplets.
The ventilation system is aimed at keeping temperatures at a cool 6-10 degrees Celsius but continually recycles the same untreated air into the room, said Exner.
“This has so far been an overlooked risk factor” in the pandemic, he told reporters, warning that the finding would have “big consequences” for other slaughterhouses as well.
He stressed that the cooling system was just “one factor” to explain the rapid spread of the virus in the slaughterhouse, and that wearing face masks and keeping a safe distance were key to controlling the transmission.