You might have heard that coronavirus can survive in the air for up to three hours.
But what does this actually mean, and how likely is it that you could catch it in the air?
(An aerosol is a tiny particle of 5 microns or less in diameter. Because these particles are tiny and light, they can remain suspended in the air, rather than quickly falling to the ground like a larger, heavier respiratory droplet.)
But this was not simply a case of the virus remaining in the air for three hours after someone coughed.
This experiment was done in a very controlled environment and the aerosols in the study were created using a high-powered machine "that does not reflect normal human cough conditions", the World Health Organisation noted in a scientific brief.
The WHO statement said aerosols could be a risk in specific circumstances, such as medical procedures like intubation (inserting a tube through a person's mouth and into their airway), disconnecting a patient from a ventilator (a machine that breathes air into and out of a person's lungs) and CPR.
But while the WHO has downplayed the risk outside of medical settings, other experts say it's impossible to rule out the possibility that the virus could be transmitted through the air in other environments.
"The fact that there are no simple methods for detecting the virus in the air does not mean that the viruses do not travel in the air," wrote Lidia Morawska from the Queensland University of Technology in a recent paper in the journal Environment International.
But there's evidence to show this is possible, particularly indoors, said Euan Tovey, an aerobiologist at the University of Sydney.
"We don't see it travelling around corners and infecting a whole aeroplane," Dr Tovey said.
"But we do see that one in the choir practice [in the US state of Washington] where 40 members, 40 out of 60 people in a choir got infected, because singing is a fantastic way of generating an aerosol."
While airborne transmission seems possible, there are some relatively straightforward precautions you can take to reduce your risk.
The physical distancing measures most of us are already observing are a great start.
Staying home as much as possible, avoiding crowded areas and standing a bit further away from the people you do come into contact with all reduce the likelihood that you'll be sharing space with someone who's infected.
Good ventilation for enclosed spaces reduces the chances of the virus hanging around in the air, said Professor Morawska, who is director of QUT's International Laboratory for Air Quality and Health.
"We don't have quantitative data about this and, of course, every environment is different," she said.
"But what I do if I go to any place, I look around. How many people are there? How, according to my judgement, is the place ventilated?
"If I see that potentially in not ventilated places, the risk is high, I don't go there."
Bringing fresh air into an enclosed space dilutes the number of viral particles in the air, scaling down the risk of you coming in contact with enough to infect you, Dr Tovey said.
"It's moving those particles on. They're not hanging around ready to be inhaled by somebody four feet away or six feet away or ten feet away or whatever it is."
But what does this actually mean, and how likely is it that you could catch it in the air?
Where did this figure come from?
A study into how long coronavirus lasts on different surfaces also looked into how long it could remain airborne, and found the virus could survive in aerosols for three hours.(An aerosol is a tiny particle of 5 microns or less in diameter. Because these particles are tiny and light, they can remain suspended in the air, rather than quickly falling to the ground like a larger, heavier respiratory droplet.)
This experiment was done in a very controlled environment and the aerosols in the study were created using a high-powered machine "that does not reflect normal human cough conditions", the World Health Organisation noted in a scientific brief.
The WHO statement said aerosols could be a risk in specific circumstances, such as medical procedures like intubation (inserting a tube through a person's mouth and into their airway), disconnecting a patient from a ventilator (a machine that breathes air into and out of a person's lungs) and CPR.
But while the WHO has downplayed the risk outside of medical settings, other experts say it's impossible to rule out the possibility that the virus could be transmitted through the air in other environments.
"The fact that there are no simple methods for detecting the virus in the air does not mean that the viruses do not travel in the air," wrote Lidia Morawska from the Queensland University of Technology in a recent paper in the journal Environment International.
How worried should I be about airborne transmission?
We still don't know exactly how many particles of virus you need to come into contact with to get infected with COVID-19, and detecting miniscule particles floating in the air is notoriously difficult, so hard data on airborne transmission is sparse.But there's evidence to show this is possible, particularly indoors, said Euan Tovey, an aerobiologist at the University of Sydney.
"We don't see it travelling around corners and infecting a whole aeroplane," Dr Tovey said.
"But we do see that one in the choir practice [in the US state of Washington] where 40 members, 40 out of 60 people in a choir got infected, because singing is a fantastic way of generating an aerosol."
While airborne transmission seems possible, there are some relatively straightforward precautions you can take to reduce your risk.
The physical distancing measures most of us are already observing are a great start.
Staying home as much as possible, avoiding crowded areas and standing a bit further away from the people you do come into contact with all reduce the likelihood that you'll be sharing space with someone who's infected.
Good ventilation lowers risk
To mitigate the risk of catching the virus through the air, there are a few extra precautions.Good ventilation for enclosed spaces reduces the chances of the virus hanging around in the air, said Professor Morawska, who is director of QUT's International Laboratory for Air Quality and Health.
"We don't have quantitative data about this and, of course, every environment is different," she said.
"But what I do if I go to any place, I look around. How many people are there? How, according to my judgement, is the place ventilated?
"If I see that potentially in not ventilated places, the risk is high, I don't go there."
Bringing fresh air into an enclosed space dilutes the number of viral particles in the air, scaling down the risk of you coming in contact with enough to infect you, Dr Tovey said.
"It's moving those particles on. They're not hanging around ready to be inhaled by somebody four feet away or six feet away or ten feet away or whatever it is."
Professor Morawska said in many instances, small changes could be enough to improve ventilation.
"If you feel that there is an air flow from another person, do something to change this," she said.
"Sometimes it's sufficient to close a door or open a door."
The amount of time you spend in an environment where there might be virus hanging around in the air is also a factor, she said.
"If you are in a situation for 10 seconds it's probably OK. But if you're in a meeting for an hour the situation could be different."
This is general advice only, but here's what the experts had to say about the potential for airborne transmission in some of the situations you have asked about.
"[Recirculation] potentially can bring back the virus into the supplied air. So ventilation as high as possible and no air recirculation."
Professor Morawska said these factors made supermarkets relatively low risk, but encouraged people to further reduce their risk by keeping their shopping time to a minimum.
There's not a lot of specific data on planes and COVID-19 specifically, but Professor Morawska said retrospective modelling showed the related SARS virus was spread on a plane.
"If you feel that there is an air flow from another person, do something to change this," she said.
"Sometimes it's sufficient to close a door or open a door."
The amount of time you spend in an environment where there might be virus hanging around in the air is also a factor, she said.
"If you are in a situation for 10 seconds it's probably OK. But if you're in a meeting for an hour the situation could be different."
Could I catch coronavirus through air conditioning?
Among the 45,000 questions the ABC has received about coronavirus since the pandemic started, the specifics of how the virus spreads have been a popular topic.This is general advice only, but here's what the experts had to say about the potential for airborne transmission in some of the situations you have asked about.
Air conditioning
Professor Morawska said that during epidemics, the recommendation was to avoid having air conditioning on recirculation mode."[Recirculation] potentially can bring back the virus into the supplied air. So ventilation as high as possible and no air recirculation."
Supermarkets
Large supermarkets tend to have good ventilation and, at the moment, the number of shoppers allowed in at any one time is being limited.Professor Morawska said these factors made supermarkets relatively low risk, but encouraged people to further reduce their risk by keeping their shopping time to a minimum.
Hand dryers in public toilets
People often ask about whether air dryers in public toilets flick particles around, but Dr Tovey said water from freshly washed hands was probably less of a concern than particles generated by flushing the toilet itself.Planes
With air travel all but completely off the table for most Australians at the moment, this is less of a factor for now.There's not a lot of specific data on planes and COVID-19 specifically, but Professor Morawska said retrospective modelling showed the related SARS virus was spread on a plane.
No comments:
Post a Comment