SARS-CoV-2 surviving 28 days on a surface ‘worst-case scenario’

Just over seven months since the coronavirus pandemic was declared, almost 38 million cases have been confirmed around the world, with more than a million reported deaths.
 
Now researchers at the CSIRO have found a piece to the puzzle as to why SARS-CoV-2, the virus responsible for COVID-19, can be so resilient.
 
The research, undertaken at the Australian Centre for Disease Preparedness (ACDP) in collaboration with the 5 Nation Research and Development (5RD) Council, found the virus can survive on common surfaces outside of its host for up to 28 days.
 
Experiments involved drying virus in an artificial mucus on six different surfaces – glass, steel, vinyl, cotton, paper and polymer banknotes – at concentrations similar to those reported in samples from infected patients, and then re-isolating the virus over a month.
 
Scientists found the virus tends to survive longer on non-porous or smooth surfaces such as glass, stainless steel and vinyl (for at least 28 days), compared to porous complex surfaces such as cotton (less than 14 days). While on banknotes, the virus lasted longer on paper notes as opposed to polymer ones, such as those used in Australia.
 
In contrast, similar experiments for influenza A have found that it survived on surfaces for 17 days.
 
Though the research does have very real implications, study co-author and ACDP Director Professor Trevor Drew told newsGP the findings represent a ‘worst-case scenario’.
 
Given direct sunlight has been shown to rapidly inactivate the virus, the experiments were carried out in the dark to remove the effect of ultraviolet light.
 
‘Certainly we know that ultraviolet light is quite effective at inactivating all viruses, and particularly coronaviruses are quite sensitive,’ Professor Drew said.
 
‘So we would expect that in direct sunlight we wouldn’t see these sort of survival times. But, nevertheless, it would have to be inside a bus or in the dark where it would be surviving for a longer period.’
 
In addition, the artificial mucus used did not contain any of the immune cells that might be present towards the end of infection.
 
‘So what we’re doing here is we’re saying this really would represent … someone who had no immunity to the virus, who was significantly affected, and was coughing up this amount of virus,’ Professor Drew said.
 
‘Certainly, we know from past studies that this does represent the amount of virus that is detected in a person when they are ill at the beginning of the disease, when they haven’t mounted an immune response. So it’s feasible, but probably represents the worst-case scenario.’
 
The research also added further weight to evidence suggesting a direct link between SARS-CoV-2 and temperature.
 
Experiments were carried out at 20⁰C (room temperature), 30⁰C and 40⁰C and showed  duration of survival drastically decreased as temperature increased.
 
‘It was really quite profound,’ Professor Drew said.
 
‘For stainless steel, [survival was] 28 days at 20⁰C and around a day at 40⁰C. If we extend this survival graph, we find that if you drop the temperature down to about 6⁰C, the virus will last about 10 times as long.’


The CSIRO’s study investigated how long SARS-CoV-2 in artificial mucous survived on six different surfaces at 20⁰C, 30⁰C and 40⁰C. (Supplied)

Professor Drew is hopeful the findings will help to explain the apparent persistence and spread of SARS-CoV-2 in cool environments with high lipid or protein contamination, such as meat processing facilities,  and to develop mitigation strategies.
 
‘Of course this effect is not just on surfaces, it’s also in the air,’ he said.
 
‘So cold air, the virus will survive for much longer, particularly if there’s no direct sunlight. So this is great news for us [in Australia] as we’re going into summer, but really bad news for Europe as they go into the winter period.’
 
 
Professor Drew says the findings further confirm the need for people to comply with COVID-safe behaviours while the virus is circulating within the community.
 
‘We should be aware of the fact that non-absorbent surfaces can act as a reservoir of the virus and that as well as being careful about face masks, we need to really keep washing our hands and keep using disinfecting wipes,’ Professor Drew said.
 
‘If you’re paying by credit card, you’re handing your card over to someone [and] that could be a potential risk. So disinfect your phone and your credit cards regularly with a disinfectant wipe. Make sure that when you’re out and about and you’re touching surfaces, such as grabbing handles on public transport, [that you’re] very alert to that.’
 
Though the transmission of SARS-CoV-2 so far appears to be primarily by aerosols, in a country like Australia where confirmed cases are significantly declining, fomite transmission may have greater implications, especially as lockdown fatigue and complacency set in.
 
‘In an environment where there’s lots of infected people, its impact is probably negligible,’ Professor Drew said.
 
‘But as we go through that phase of reducing numbers of infected people in our environments, so the role of contaminated surfaces is likely to be more important, and therefore just stresses again how even when there’s not very many cases, we must continue to behave as if our environment is contaminated for a considerable period.
 
‘It’s really, really important that we reinforce this message that just because there are only a few infected people out there, it really does still present a significant risk.
 
‘We have to make sure that we think about our behaviours. I was in Coles on Saturday and I saw someone licking her fingers to open a plastic bag to put some vegetables in. Little things like that can result in a recrudescence of the infection.’
 
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