Are you more likely to catch coronavirus from surfaces or from droplets in the air?
What we know about airborne transmission of coronavirus has evolved significantly since the start of the pandemic.
The WHO recently ramped up its advice on aerosol spread.
But what about surfaces?
We have received many audience questions on the topic recently including:
Is surface contact a cause of community transmission?
How should you handle items that come from hotspots?
How long can the virus survive in a fridge or freezer?
So what’s the latest thinking on this issue? Unlike evidence around aerosol transmission, not much has changed in regards to advice about surfaces.
How long can coronavirus stay on surfaces?
Like flu and SARS, research tells us coronavirus is most likely spread by the direct transmission of respiratory droplets from someone coughing or speaking towards you, says Mary-Louise McLaws, epidemiologist and advisor to the World Health Organisation (WHO).
Surface transmission is considered a less common mode of spread, according to the WHO.
A widely accepted study in the New England Journal of Medicine published in March is still considered to provide the best evidence of how long coronavirus can last on different types of surfaces.
Under experimental conditions it found:
The virus could still be detected on stainless steel and plastic after 72 hoursNo viable SARS-CoV-2 could be detected on a cardboard surface after 24 hoursNo viable SARS-CoV-2 could be detected on a copper surface after four hours
There is no current evidence that anyone has become infected by ingesting the virus in, or on, food or drink.
So what is the risk of getting infected from surfaces?
Based on what we know about other respiratory diseases, the Centre for Disease Control (CDC) says it’s possible a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose or possibly their eyes.
“But this isn’t thought to be the main way the virus spreads,” the CDC says.
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Susy Hota, an infection prevention and control expert at the University of Toronto, says much has been learnt about surface spread as the pandemic unfolded.
“Early research showed the virus could survive on surfaces for up to six days, which was worrisome,” she says.
“But it’s probably not as big of a risk as we initially thought.”
There is still no evidence in any COVID-19 studies that anyone has contracted the virus from a surface alone.
Ian Mackay, a virologist at the University of Queensland, says the growing evidence about aerosol transmission may mean surface transmission becomes a more minor risk.
The problem is we often can’t definitively say how someone becomes infected, Dr Mackay points out.
Importantly, the risk is not zero and surface transmission could play a role when we see COVID-19 spread through a household.
When people become infected in a shared environment it’s likely a mix of breathing and coughing around each other and touching the same surfaces, says Catherine Bennett, head of epidemiology at Deakin University.
While washing your hands is imperative when you use a surface immediately after someone, maintaining physical distance is just as important, Professor Bennett says.
Surfaces touched by high volumes of people are still of the most concern.(Supplied: Federal Group)
The big question remains — can we pick up a high enough dose of coronavirus from a surface to actually become infected?
The short answer is we won’t know until droplet experiments are conducted with COVID-19-positive patients in a safe way.
“Until somebody can do some really clever studies … there aren’t going to be any really solid 100 per cent answers on surfaces,” Dr Mackay says.
Without that, all we have are lab-based scenarios, which don’t replicate the complications of the real world.
In the past, volunteers would be infected with a virus for research purposes but Professor Bennett says that is not ethical considering all that remains unknown about COVID-19.
“We still don’t know what COVID-19 can do to you in another six months or 10 years,” she says.
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Read moreHow can you reduce your risk?
The actual likelihood of contracting coronavirus from touching the same surface as an infected person may not be known for some time but there are ways to minimise potential exposure.
Don’t split hairs about handling an object that has come from a hotspot area, Dr Mackay says.
“Just make sure you wash your hands in between touching that thing and then touching your face.
“And if you are really worried leave the object somewhere to sit for 24 hours or 48 hours and you will have knocked the chance of infection down incredibly low.”
Remember, parcels are subject to sun, wind and dust, which all lower the virus’s ability to stay alive.
Don’t stress too much about picking up coronavirus from your mail or groceries, instead think about frequently touched surfaces like door handles and lift buttons, Professor Bennett says.
“This is especially true in really contained environments where people aren’t just touching the same thing but they’re in close proximity too. So keep washing those hands.”