Cleaning a surface with disinfectant spray.
How long does Coronavirus last on surfaces? And which disinfectants are most effective at cleaning them?
Those two questions are important not only for healthcare centres but any public place with a lot of activity — locations where you’ll frequently touch surfaces such as door handles with your hands. You might then potentially infect yourself by touching your face, which happens far more often than you think.
So how long can SARS-CoV-2 survive on a non-living surface? Under the carefully-controlled conditions inside of a laboratory, one early study found that it remains stable on metals and plastic for three days. Outside a lab, however, the virus might last considerably longer: its genetic material could be detected on surfaces 17 days after a cruise ship was empty of passengers (although it’s not clear whether that material represents infectious virus particles).
To answer both questions, we turn to a recent systematic review of the scientific literature published in the Journal of Hospital Infection, led by Günter Kampf of the Institute of Hygiene and Environmental Medicine in Germany. The review involved scouring a database for studies that had examined how long coronaviruses can persist on surfaces and/or the effect of disinfectants. The search returned 22 results.
The review, entitled ‘Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents’, aimed to summarise all the available data and focused on viruses that infect humans — including those behind MERS and SARS — as well as coronaviruses in other animals (dogs, pigs and mice).
According to the review, viruses can survive on surfaces for anywhere between 2 hours to over a month. It found that most data came from HCoV-229E, a strain of human coronavirus that causes the common cold. At room temperature, HCoV remains infectious on various materials — everything from metal and glass to Teflon and PVC — for up to 9 days. Generally, higher temperatures or humidity would enable coronaviruses to last longer.
What about SARS-CoV-2 specifically? Although there were no data on the Covid-19 coronavirus, its close relative SARS-CoV-1 was found to persist longer when more virus particles were present on a surface.
So what’s the most effective way to disinfect surfaces? In the studies analysed by the review, experiments on efficacy were mainly performed through ‘suspension test’, which is when the germ and biocidal agent are put together in a solution for a certain amount of time, after which the microbe is extracted and tested to see whether it’s still alive and capable of infecting.
The review revealed that HCoV can be efficiently inactivated within 1 minute by biocidal agents found in many common cleaning products, including concentrations of 62% ethanol, 0.5% hydrogen peroxide and 0.1% sodium hypochlorite, or bleach. Other common agents, such as benzalkonium chloride, were found to be much less effective at killing coronaviruses.
Bleach is typically produced by diluting 5% sodium hypochlorite with water to produce a 1:100 dilution (0.05%). But in order to be effective within 1 minute, the reviewers suggest that the concentration should be doubled to give a 1:50 dilution (0.1%). This recommendation is based on findings from studies and can be immediately applied when you next disinfect a surface.
Cleaning with disinfectants helps reduce infections because respiratory viruses can be transmitted to the face (where germs invade) from contaminated surfaces, usually via the hands, known as ‘self-inoculation’ through contact transmission.
Surprisingly, the review didn’t find data on the extent to which coronaviruses are transmitted from surfaces to hands. It points out that touching a surface contaminated with influenza A virus for only 5 seconds transferred 32% of virus particles to the hands, whereas a mere 1.5% of the viral load is transmitted after direct contact with the flu virus’ cousin, parainfluenza-virus 3. That means that we might not be able to extrapolate from HCoV to SARS-CoV-2.
Clearly there’s a lot we still don’t know about how long Coronavirus lingers on the surfaces around us, but at least we understand more about how to clean them.