Mobile phone screens, bank notes and stainless steel can harbour the coronavirus that causes COVID-19 for up to 28 days, according to new CSIRO research that may force public-health authorities to revise their recommendations around surface disinfection.
The scientists, working at the CSIRO’s Australian Centre for Disease Preparedness in Geelong, inoculated concentrations of the SARS-CoV-2 virus – roughly equivalent to the typical amount of virus excreted by an infectious COVID-19 – onto a range of surfaces at a range of temperatures.
At room temperature (20 degrees), the scientists reported in a new article in Virology Journal, half of the viral load could still be detected, on average 1.7 to 2.7 days later.
When heated to 40 degrees, the virus half-life was decreased to just a few hours.
Most worryingly, however, was the finding that at 20 degrees “viable virus” could still be isolated from non-porous surfaces – such as glass, stainless steel, and paper and polymer banknotes like those used in Australia – as much as 28 days later.
That means you could theoretically be exposed to SARS-CoV-2 by using an ATM, supermarket self-service checkout, airport check-in kiosk or other public touchscreen device – if it had been used by a COVID-19-positive patient at any time in the last four weeks.
The virus could also be transmitted if you shared a mobile phone or office phone that had been used by a COVID-19-positive patient within the past few weeks, and had not been properly disinfected.
Porous materials, such as cotton used in clothing, reduced viral loads much more quickly and the virus lasted a maximum of 14 days, with detectable amounts dipping quickly in the first few days.
The results “demonstrate SARS-CoV-2 can remain infectious for significantly longer time periods than generally considered possible,” the team, led by CSIRO biorisk pathogen specialist Shane Riddell, concluded.
And while environmental conditions were carefully controlled – samples were kept in the dark, for example, to eliminate the potential disinfectant effect of sunshine UV light – the “high” amount of virus inoculated onto the test surfaces “represents a plausible amount of virus that may be deposited on a surface”.
A changing understanding of risk
Viral infection of fomites – contaminated objects or surfaces – has been extensively studied but the extended timeframes in the new CSIRO study, and the fact that the viral loads persisted at common real-world temperatures, suggest that surface-based transmission remains a significant potential problem.
Early concerns about surface transmission led heavily trafficked stores like Woolworths and Coles to implement aggressive surface-cleaning policies that included checkouts and trolleys, while retailers have actively discouraged the use of cash as banks encouraged adoption of contactless payments.
These policies echo Australian Department of Health recommendations that citizens clean and disinfect “surfaces you use often such as benchtops, desks and doorknobs” as well as “objects you use often such as mobile phones, keys, wallets and work passes”.
Yet official global guidance offers a different perspective, with a World Health Organisation (WHO) literature review noting that virus transmission “may also occur indirectly through touching surfaces in the immediate environment or objects contaminated with virus from an infected person, followed by touching the mouth, nose, or eyes.”
Despite this possibility, however, WHO suggests that “there are no specific reports which have directly demonstrated fomite transmission” – a perspective echoed by Centres for Disease Control guidelines that suggest that “transmission of novel coronavirus to persons from surfaces contaminated with the virus has not been documented” and that respiratory droplets such as sneezes are a much more common infection vector than touching surfaces.
“Cleaning of visibly dirty surfaces followed by disinfection is a best practice measure for prevention of COVID-19 and other viral respiratory illnesses in households and community settings,” the CDC advises.
Although “fomite transmission is considered a likely most of transmission”, the WHO notes, it can be hard to distinguish between virus that is passed from infected people and virus that is passed from surfaces that they have touched.
“People who come into contact with potentially infectious surfaces often also have close contact with the infectious person,” it advises, “making the distinction between respiratory droplet and fomite transmission difficult to discern.”