Our COVID-19 research includes SARS-CoV-2 on surfaces. We’re conducting the work within our highly secure Biosecurity Level 4 laboratories at the Australian Centre for Disease Preparedness (ACDP).
From the moment you turn off your morning alarm, to the time you hit the pillow, your life is full of surfaces. Swiping through your phone, opening doors, putting in your PIN – there are many you don’t think twice about touching.
But SARS-CoV-2, the virus that causes COVID-19, will likely change the way we all think about, and interact with, surfaces forever. Our peer-reviewed study published in Virology Journal reveals new information about the virus and how it behaves on surfaces.
Understanding SARS-CoV-2 on surfaces
From analysing sewage to testing face masks, our research has been contributing to the global battle against COVID-19.
At this stage of the pandemic, researchers do not fully understand the role contaminated surfaces play in the transmission of SARS-CoV-2. To improve our understanding of how this new virus behaves, our researchers studied the survival rates of infectious SARS-CoV-2, dried in an artificial mucous solution, on six common surfaces.
We conducted the experiment at three different temperatures, 200C, 300C and 400C, with the relative humidity kept at 50 per cent. The surfaces used in the study were stainless steel, glass, vinyl, paper and polymer banknotes, and cotton cloth. These are examples of high contact surface areas such as glass on touchscreens and stainless steel doorknobs.
A droplet of fluid containing the virus at concentrations similar to levels observed in infected patients was dried on multiple small test surfaces and left for up to 28 days. At various time periods, the virus was recovered and placed in tissue culture cells to observe if any infectious virus remained.
Impact of temperature on virus
At 20°C, the virus was extremely robust. We were able to recover infectious material after 28 days from the smooth (non-porous) surfaces. These are stainless steel, glass, vinyl and paper and polymer banknotes.
The length of time infectious virus was able to survive on the porous material (cotton cloth) was much shorter. On cloth, we were unable to detect any viable virus past 14 days.
At 30°C infectious virus did not survive beyond seven days on stainless steel, money (polymer banknotes) and glass. However, on vinyl and cotton cloth, infectious material was not detectable beyond three days.
At 40°C virus was inactivated much faster. Infectious SARS-CoV-2 was detectable for less than 16 hours for cotton cloth. While on glass, paper and polymer notes, and stainless steel it was detectable for up to 24 hours, and 48 hours for vinyl.
How long SARS-CoV-2 survived on five different surfaces at three temperatures, 20°C, 30°C and 40°C.
How many particles can cause an infection?
It generally takes more than one virus particle to infect a person and make them sick. We call the number of virus particles that can cause infection the “infectious dose”. This dosage differs between different viruses and is usually quite large.
Researchers do not yet know the infectious dose of SARS-CoV-2. But, from our knowledge of related viruses, we estimate it is around 300 particles. If the virus was placed (on smooth surfaces) at standard mucus concentrations of an infected person, enough virus would easily survive for two weeks to be able to infect another person.
Further research on this topic is necessary. However, our findings indicate the 28-day sample would not contain enough viable virus to infect a person.
Whether virus particles on a surface can infect someone is dependent on several conditions. Outside of the body, SARS-CoV-2 virus particles gradually become inactive over time. The time it takes for viruses to naturally inactivate depends on many factors. The makeup of the virus itself, the type of surface it is on and whether the virus is liquid or dried can impact the time it remains viable. Environmental conditions such as temperature, exposure to sunlight and humidity also play a part.
Cash or card? A droplet of liquid containing the SARS-CoV-2 virus on a $5 note.
How virus transmission works
In general, we know people deposit viruses onto surfaces by coughing or sneezing. They are also readily transferred between contaminated skin and surfaces.
The results from our study confirm that high-contact surfaces may pose a risk. These are the type of surfaces that have a significant number of different people touching them each day. They include bank ATMs, handrails, door handles, elevator buttons, supermarket self-serve check-outs and money.
While we can’t yet answer the likelihood of developing COVID-19 from surfaces, we do know the SARS-CoV-2 virus can’t penetrate skin. To catch the disease, you would first need to introduce the virus into your mouth, nose or eyes. Our findings reinforce the message that you should avoid touching your eyes, nose and mouth and keep washing your hands. It’s also important to be careful when removing facemasks as the virus can survive on the outside where you could transfer it to your hands.
Building our understanding of COVID-19
Although we still don’t know how much virus it takes to infect someone, our research is forming a better understanding of how this new virus behaves.
Our knowledge that the virus survives longer at colder temperatures may also help to explain the spread of SARS-CoV-2 in environments such as meat processing facilities.
Our research will help to provide insight into the risks associated with COVID-19. And can help with the development of procedures for minimising the chances of virus spread via surfaces.
22nd October 2020 at 9:28 pm
Thank you for the interesting and accessible article. Your reported active virus durations are substantially longer than those reported from testing in the US and Europe, earlier in the year. Were your samples on ordinary house-hold surfaces and in ordinary house-hold conditions? Or were they kept in the dark, as was reported on Radio National of one study recently done in Australia?
23rd October 2020 at 1:29 pm
Hi Dimity, the purpose of this study was to measure the survival of the virus at different temperatures in the mucous-type matrix that is present in the lungs and upper respiratory tract of people. It was important to reduce the number of variables, which might impact on survival, such as sunlight. Other studies have indicated sunlight can rapidly inactivate the virus, which is why we conducted the experiment in the dark.
Thanks,
Team CSIRO
22nd October 2020 at 7:06 pm
Presumably the mucous solution is the source of “nutrient” for the virus.
How much mucous was used in each of the tests? A droplet could be an unrealistically large amount compared to a real life situation. The more the nutrient-the longer the virus can survive presumably – a porous surface would absorb most, if not all, the nutrient, thus depriving the virus of such, whereas the nutrient would remain on a non-porous surface, thus extending the life of the virus.
I would welcome your comments.
23rd October 2020 at 1:30 pm
Hi there, thanks for your question. In this experiment, the viral load in the artificial mucous solution was similar to levels observed in infected patients. The aim was to represent the “worst case scenario’ of the likely viral load and survival of virus excreted by someone newly infected.
Thanks,
Team CSIRO
22nd October 2020 at 4:27 pm
Hi there, this is a nice communication of some very important research. What I find interesting straight away is the type of surface and surviabiity of the virus, and also the impact of temperature. I think about the temperature of surfaces that exposed to sunlight there the temperature might be much greater than an amibient 20degC. Was timber studied?
22nd October 2020 at 9:20 am
Thank you CSIRO research team for providing another piece of information to inform covid management responses. You have done a great job using detect/non detect analysis for COVID-19 virus by replicating original doses and conditions likely to occur in practice and developing a way to recover virus. Normally environmental risk management for pathogens requires log-removal times. Do we currently have a way of quantifying number of viable viruses, which in combination with research on the infectious dose could feed more directly into quantitative microbial risk assessment? Your work shows that such log-removal measurement is warranted and I wish you well with the work in front of you, which is fundamental, internationally relevant and deserves strong support. Congratulations on your progress.
20th November 2020 at 11:44 am
Hi Peter, thank you for your support of our work. We are aware that research on discovering what is an infectious dose of SARS-CoV-2 is ongoing but currently there is no information available.
A number of discs of each of the different materials were first contaminated with a known amount of virus suspended in the artificial mucous and placed in the dark at different temperatures. At different time points, three discs of each material were removed and examined for live virus.
Our detection method involved rinsing the surface with a small amount of fluid, at different time points over a 21-day period. We then made sequential 10-fold dilutions of this fluid and then mixed these different dilutions will cells, so that any live virus would infect them. In this way, we were able both to demonstrate the presence of live virus and calculate the amount, as the “tissue culture infectious dose” at each time point. As you see from our graphs, the amount of infectious virus steadily declined over time at different rates, depending on the surface and the temperature.
Thanks,
Team CSIRO
22nd October 2020 at 7:42 am
Clarification please, The TV news said at the end that all your testing was done in the dark. I can see the small print reference to no ultraviolet light. Is this not such a vast difference to the real world that the headline should be changed or better still should the test be redone with some modest sunlight and then recommend this time as the virus killer.
22nd October 2020 at 12:24 pm
Hi Michael, thanks for your comment. The purpose of this study was to measure the survival of the virus at different temperatures in the mucous-type matrix that is present in the lungs and upper respiratory tract of people. It was important to reduce the number of variables, which might impact on survival, such as sunlight. Other studies have indicated sunlight can rapidly inactivate the virus, which is why we conducted the experiment in the dark.
Thanks,
Team CSIRO.