


Hassan Vally, La Trobe University

A lot has happened over the past year, so you can be forgiven for not having a clear memory of what some of the major concerns were at the beginning of the pandemic.

However, if you think back to the beginning of the pandemic, one of the major concerns was the role that surfaces played in the transmission of the virus.

As an epidemiologist, I remember spending countless hours responding to media requests answering questions along the lines of whether we should be washing the outside of food cans or disinfecting our mail.

I also remember seeing teams of people walking the streets at all hours wiping down poles and cleaning public benches.

But what does the evidence actually say about surface transmission more than 12 months into this pandemic?

Before addressing this, we need to define the question we’re asking. The key question isn’t whether surface transmission is possible, or whether it can occur in the real world — it almost certainly can.

The real question is: what is the extent of the role of surface contact in the transmission of the virus? That is, what is the likelihood of catching COVID via a surface, as opposed to other methods of transmission?

The evidence is minimal

There’s little evidence that surface transmission is a common way in which the coronavirus is spread. The main way it’s spread is by the air, either by larger droplets via close contact, or by smaller droplets called aerosols. As a side note, the relative role these two routes play in transmission is probably a much more interesting and important question to clarify from a public health perspective.

One of the best commentaries on COVID surface transmission was published in the journal Lancet Infectious Diseases in July 2020 by Emanuel Goldman, a professor of microbiology from the United States.

As he described, one of the drivers for the exaggerated perception of the risk of surface transmission was the publication of a number of studies showing SARS-CoV-2 viral particles could be detected for long periods of time on various surfaces.

You probably saw these studies because they received enormous publicity worldwide and I remember doing numerous interviews in which I had to explain what these findings actually meant.

As I explained at the time, these studies could not be generalised to the real world, and in some instances the media releases accompanying them tended towards overstating the significance of these findings.

The key issue is that as a general principal the time required for a population of microoganisms to die is directly proportional to the size of that population. This means the greater the amount of virus deposited on a surface, the longer you will find viable viral particles on that surface.

So in terms of designing experiments that are relevant to public health, one of the more important variables in these studies is the amount of virus deposited on a surface — and the extent to which this approximates what would happen in the real world.

If you understand this, it becomes apparent that a number of these virus survival studies stacked the odds of detecting viable virus by depositing large amounts of virus on surfaces far in excess of what would be reasonably expected to be found in the real world. What’s more, some of these studies customised conditions that would extend the life of viral particles, such as adjusting humidity and excluding natural light.

Although there was nothing wrong with the science here, it was the real world relevance and the interpretation that was amiss at times. It’s notable that other studies which more closely replicated real world scenarios found less impressive survival times for three other human coronaviruses (including SARS).

It’s important to note we’re relying on indirect evidence in assessing the role of surface transmission for the coronavirus. That is, you can’t actually do an ethical scientific experiment that confirms the role surface transmission plays because you’d have to deliberately infect people. Despite being such a seemingly straightforward question, it’s surprisingly difficult to determine the relative importance of the various transmission pathways for this virus.

What we have to do instead is look at all of the evidence we do have and see what it’s telling us, including case studies describing transmission events. And if we do this, there isn’t a lot out there to support surface transmission being of major importance in the spread of COVID.

We could save a lot of time and money

We need to put the risks of exposure to SARS-CoV-2 via the various modes of transmission into perspective, so we focus our limited energy and resources on the right things.

This isn’t to say surface transmission isn’t possible and that it doesn’t pose a risk in certain situations, or that we should disregard it completely. But, we should acknowledge the threat surface transmission poses is relatively small.

We can therefore mitigate this relatively small risk by continuing to focus on hand hygiene and ensuring cleaning protocols are more in keeping with the risk of surface transmission.

In doing this, we can potentially save millions of dollars being spent on obsessive cleaning practices. These are probably providing little or no benefit and being done solely because they’re easy to do and provide the reassurance of doing something, thereby relieving some of our anxieties.The Conversation

Hassan Vally, Associate Professor, La Trobe University


How worried should I be about news the coronavirus survives on surfaces for up to 28 days?


Lara Herrero, Griffith University and Eugene Madzokere, Griffith University

During a typical day, we touch the surfaces of many different objects, often without noticing: money, phones, door handles, elevator buttons, cups, desks, keyboards, petrol pumps and shopping trolleys.

Objects with surfaces that carry pathogens (such as bacteria or viruses) can pass on infections when we touch them. So it makes sense contact with these contaminated surfaces (often called “fomites”) might increase our infection risk.

Now a study published by CSIRO researchers suggests SARS-CoV-2, the virus that causes COVID-19, can survive up to 28 days on common surfaces.

So, is this cause for panic? The answer is, not necessarily.

What did the study find?

The researchers applied SARS-CoV-2 to Australian plastic banknotes, paper banknotes, stainless steel, glass, vinyl and cotton cloth.

They exposed the objects to three different temperatures — 20℃, 30℃ and 40℃ — all in the dark and with 50% humidity. They then measured the amount of surviving live virus over time.

At 20℃, the virus survived longer (up to 28 days) on smooth surfaces, such as glass and banknotes (both plastic and paper), than on porous surfaces such as cotton.

At 30℃ the virus was not detected beyond day seven on any surface except paper banknotes, where it survived up to day 21.

At 40℃, the virus was rapidly inactivated, meaning it couldn’t cause infection.

Read more:

What does this mean for our daily routine?

The study was designed to mimic the spread of the virus indoors on surfaces under dark conditions only. In Australia, 28 days of darkness would not be considered normal.

However, this is the first study to show long-term survival (28 days) of the virus on non-porous surfaces such as glass, steel and banknotes.

Previous studies indicated the virus survives for much shorter periods. This is from a few hours to less than seven days, inside, at temperatures under 25℃, and in lit environments with varying humidity.

Although the CSIRO findings are scientifically significant, their relevance to the everyday transmission of the virus remains uncertain.

Where does this leave us?

Many of the object surfaces we touch certainly deserve consideration as sources of SARS-CoV-2 transmission. However, how long the virus survives on them depends on several environmental and other factors, not all of which researchers have sufficiently studied.


Could exposing the object surfaces to light have affected the results? At this stage, we just don’t know.

Other researchers have looked at the ability of a form of ultraviolet light (known as UVC) to inactivate the virus.

However, this form is not abundant in sunlight. So we cannot simply leave objects (possible fomites) in the sun hoping to deactivate any potential viruses hitching an unwelcome ride.

Read more:
Ultraviolet radiation is a strong disinfectant. It may be what our schools, hospitals and airports need

This and other research means we still don’t fully understand the impact of sunlight or other sources of light on the viability of the virus on common objects under everyday conditions. This could be in the home, workplaces or shopping centres, or in enclosed spaces such as in cars or on public transport.

Most of the research so far on using light to inactivate the virus has focused on hospitals or other controlled settings, and using artificial light.


Humidity is also likely to play a role in the survival of SARS-CoV-2, but there is no certainty on what the role is.

Most studies analysing humidity have been observational, meaning researchers are observing the spread of virus in a population under certain weather conditions.

So far observations are that increasing humidity may be worse for virus survival.

This has also been demonstrated in a laboratory, with increasing humidity decreasing the virus’ survival on fomites. However we’re not certain whether this is relevant to everyday life.

Type of secretion

We know the virus is mainly transmitted through the air, by inhaling respiratory secretions containing the virus.

While there is ongoing debate about whether the virus is spread via droplets or is airborne, this is merely a debate on how small a particle can be while still successfully transferring the virus and causing infection.

Research to conclusively prove SARS-CoV-2 can be transmitted via micro particles (5 micrometres or less, the definition of airborne transmission) is still ongoing.

For now, if a SARS-CoV-2 infected person coughs, sneezes or wipes respiratory secretions onto an object, this object may become a fomite.

Read more:
Is the airborne route a major source of coronavirus transmission?

In a nutshell

The CSIRO study furthers our understanding of SARS-CoV-2. However, it does not suggest fomites are a significantly greater source of infection than what we are currently managing with existing COVID-19 hygiene practices.

We need to continue frequently washing and sanitising our hands and surfaces, wearing personal protective equipment such as masks if in high-risk situations or when mandated, and physically distancing.The Conversation

Lara Herrero, Research Leader in Virology and Infectious Disease, Griffith University and Eugene Madzokere, PhD Candidate in Virology, Griffith University



Manuel Bruque/EPA

Ian M. Mackay, The University of Queensland and Katherine Arden, The University of Queensland

Like the other 200 or so respiratory viruses we know of, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the new coronavirus, infects the cells of our airways.

It causes a range of signs and symptoms, or none at all. It can spread easily from person-to-person, and can be coughed into the air and onto surfaces.

Viruses only replicate inside a living cell – outside the cell, they’re on a path to either infect us, or their own destruction. How long a virus survives outside a cell varies.

Researchers found SARS-CoV-2 remains infectious in airborne droplets for at least three hours. This doesn’t mean infected humans produce enough virus in a cough to infect another person, but they might.

Wes Mountain/The Conversation, CC BY-ND

We think the virus also spreads by touch. Hard, shiny surfaces such as plastic, stainless steel, benchtops, and likely glass can support infectious virus, expelled in droplets, for up to 72 hours. But the virus rapidly degrades during this time. On fibrous and absorbent surfaces such as cardboard, paper, fabric and hessian, it becomes inactive more quickly.

How can we reduce risk from surfaces and objects?

Frequently touched surfaces are all around us. Benches, handrails, door handles – they are in our homes, on our way to work, school, play, shop, and every other destination. There’s a risk of contaminating these surfaces if we touch them with virus-laden fingers, and a risk we’ll contract the virus from such surfaces.

Think of your hands as the enemy. Wash them well, and much more often than usual. Between hand-washing, avoid constantly touching the mucous membranes that lead to your airways. Basically, try not to rub your eyes, pick your nose, or touch your lips and mouth.

Read more:
Can I get coronavirus from mail or package deliveries? Should I disinfect my phone?

Taking precautions through small actions

We’re already seeing engineering initiatives to help combat the virus’s spread. In Sydney, pedestrian crossings have been automated so people can avoid touching the buttons.

To slow the spread of SARS-CoV-2, assume everything outside your home is potentially contaminated, and act accordingly. So don’t touch your face, sanitise frequently while you are out, and wash your hands and clean your phone once home.

While it’s best to stay home, keep these tips in mind if you must leave the house.

• Going shopping

Grocery shopping requires touching surfaces and items, including trolleys and baskets. Sometimes sanitiser or antibacterial wipes are available for hands and handles at the store entrance – but they’re often not, so bring your own (if you can get some). It probably doesn’t matter what type of bag you use, but have a plan for how to avoid bringing the virus into your home.

• Making payments

Cards and cash could transfer the virus to your hands. That said, card payment is probably lower risk because you retain the card and don’t have to touch other people. But wherever possible, contact-free bank transfers would pose the least risk.

• Handling and eating fresh and canned food

SARS-CoV-2 is inactivated at temperatures well below those required in the process of canning food, so canned food is free of it. For freshly packaged food, risk depends on whether the person doing the packing was sick or not. If you are concerned, stick with food that can be cooked, peeled or washed in mild soapy water, and thoroughly rinsed.

Read more:
Can coronavirus spread through food? Can anti-inflammatories like ibuprofen make it worse? Coronavirus claims checked by experts

While evidence is weak, we know soap and water should inactivate SARS-CoV-2 on food – but this will work better on foods with a shinier, harder outer surface, compared to foods that have been cut or have softer surfaces, such as strawberries and raspberries. If you decide to wash any food with soap, make sure all the soap is removed.

• At the park

Avoid equipment that is likely used a lot, including play equipment and water fountains. It would be safer to kick a ball around or play on the grass, rather than use swings. Sandpits hold horrors other than SARS-CoV-2.

• Takeaway and deliveries

When getting takeaway food, or for businesses offering it, avoid plastic containers and use more fibrous materials such as cardboard, paper and fabric for packaging. Researchers found no infectious SARS-CoV-2 on cardboard after 24 hours.

Also, avoid proximity to servers and delivery people, and opt for contactless delivery whenever you can.

• Public transport, escalators, elevators and bathrooms

Frequently touched hard, shiny surfaces such as lift buttons and handle bars in trams are a big risk, more so than fabric seats, or taking the stairs. Even the most high-tech overseas surface cleaning efforts are intermittent, so you’ll need to take responsibility for yourself. Also, after using public bathrooms, wash your hands well.

Calm and calculated

It’s important to be calm, realistic and not focus on single events or actions once you step outside. You can’t account for everything.

Think more about the risk of the entire task rather than the many small risks encountered during the process. A silver lining in taking such precautions is that you’ll also reduce your risk of catching the flu this season.

It’s also important to keep your home clean. You can use diluted bleach, detergents or alcohol solutions on surfaces. Queensland Health has more information.

Read more:

For items that are hard to clean, sunshine may be valuable. Leave your shoes outside, soles up, in the sun. Coronaviruses begin degrading quickly in temperatures higher than 56 degrees Celsius, and in direct UV light.

Ultimately, the best ways to avoid SARS-CoV-2 infection are primitive ones – sanitise your hands and stay away from others. Physical distancing remains the most effective measure to slow the progression of this pandemic.The Conversation

Ian M. Mackay, Adjunct assistant professor, The University of Queensland and Katherine Arden, Virologist, The University of Queensland
