Coronavirus may survive on outdoor surfaces for longer in autumn, US study suggests
- Researchers find it could linger for up to a week outside in lower temperatures and humidity – more than the one to three days in summer
- That could ‘potentially contribute to new outbreaks’ in northern hemisphere, they warn in non-peer-reviewed paper
Researchers found that in lower temperatures and humidity, the virus could, for example, remain on a hiker’s jacket if it was outside for a week – and remain infectious for that time – whereas in summer its lifespan was estimated to be one to three days.
The prolonged survival of the virus on surfaces in autumn could “potentially contribute to new outbreaks”, the team led by Juergen Richt, professor of veterinary microbiology at Kansas State University, wrote in a non-peer-reviewed paper posted on preprint website bioRxiv.org on Monday.
They believed the virus would also survive for longer indoors in colder and less humid conditions. The study found it had an average half-life – or rate of decay – of nearly eight hours on a stainless steel doorknob, or nearly 10 hours on a window, which was about to twice the duration in summer.
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The coronavirus, which causes the disease Covid-19, has adapted well to humans. But to survive outside its human hosts – it spreads through respiratory droplets and contaminated surfaces – the pathogen is believed to prefer lower temperatures and humidity.
For the study, Richt’s team used climate data from America’s Midwest to recreate artificial seasons in biosafety chambers. Temperature was controlled at 13 degrees Celsius and 66 per cent relative humidity for spring and autumn, while for summer it was kept at 25 degrees and 70 per cent.
The virus was then applied to the surface of 12 materials people come into contact with every day, such as cardboard, concrete, rubber, gloves and N95 masks. The aim was to find out if the viability of the virus changed with the season.
Earlier in the pandemic, the research community had hoped the spread of the virus would slow in summer, believing it would be less likely to stay in the air in warmer weather.
But the resurgence of infections in many areas – especially the United States, the worst-hit country where nearly 80,000 cases per day were recorded at the peak of summer – raised the question of whether there was any seasonal impact at all.
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The result of the Midwest study “clearly demonstrates that the virus survives longer under spring/fall not summer conditions”, the researchers said in the paper.
That trend was observed on all materials tested, to varying degrees. Out of all of them, the virus survived longest on Tyvek, a synthetic material used in everything from home insulation to personal protective equipment and outdoor wear, with a half-life of up to 45 hours.
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Autumn could also see a rise in other infectious diseases such as flu, which might further stretch health care systems. It could also result in patients having multiple infections that make their symptoms worse, recent studies have warned.
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Richt and his colleagues urged people to maintain the “practice of good personal hygiene and regular disinfection of potentially contaminated surfaces” to prevent the spread of the virus.
The study follows a warning earlier this month from the US Centres for Disease Control and Prevention of the potential for the situation to get worse in autumn. Director Robert Redfield said people needed to do four things: “wear a mask, social distance, wash your hands and be smart about crowds”. Otherwise, he said, it could be “the worst fall, from a public health perspective, we’ve ever had”.
