Risk of catching COVID-19 from touching contaminated objects such as groceries is ‘negligible,’ researchers say
Emanuel Goldman’s mother-in-law was driving him up the wall. “‘Wipe down the groceries. Wipe down the handles of the bags from the people who delivered the food,’ ” he recalls her saying.
Her demands prompted Dr. Goldman, a professor of microbiology, biochemistry and molecular genetics at Rutgers University, to dig into the scientific literature on the transmission of human coronaviruses. What he found confirmed his suspicions: The risk of catching COVID-19 from touching contaminated surfaces and objects – or what scientists call fomites – is “negligible,” he said.
Dr. Goldman is among a camp of researchers who now believe the chances of getting COVID-19 from fomites are probably much smaller than originally thought. Although they support hand hygiene and the cleaning and disinfecting of surfaces, they suggest other measures, such as physical distancing and wearing masks, play a far bigger role in preventing the spread of the new coronavirus.
And if they’re right, that means pushing elevator buttons, touching door handles and allowing children on outdoor playground equipment are all less risky than previously believed.
“You’ve [still] got to protect yourself,” Dr. Goldman said, emphasizing people should not ignore the seriousness of COVID-19. “But you’ve got to protect yourself correctly – not by worrying about surfaces, but by worrying about what you breathe.”
In a comment published by The Lancet earlier this month, titled Exaggerated Risk of Transmission of COVID-19 by Fomites, he noted that studies upon which assumptions about surface contamination are based do not reflect real-life situations.
For example, multiple studies suggest human coronaviruses can survive on surfaces for several days. However, in these studies, researchers used amounts of these viruses that are several orders of magnitude larger than what people would normally encounter, he said.
Some studies used one million to 10 million infectious virus particles for each sample. That would be the equivalent of collecting droplets from 10,000 to 100,000 infected people and applying them to one small area, Dr. Goldman said.
“It’s absurd,” he said, noting he doesn’t dispute the quality of this research. Rather, “it just has nothing to do with the real world.”
In studies using much smaller quantities, human coronaviruses are shown to survive for much shorter amounts of time. In one study, he said, they survived between one to three hours. In a different study, which he said better reflected the amount of virus people would typically encounter, no infectious virus particles were found after about an hour.
Another problem with these types of studies is many of them looked for the presence of what’s called viral RNA, or the nucleic acid of the virus, but not necessarily the presence of actual viable virus – that is, virus that’s able to cause infection, said Gerald Evans, chair of the division of infectious diseases at Queen’s University.
RNA is a sticky molecule, he said, explaining it adheres to surfaces and is difficult to get rid of.
“Physically, it looks like a goo,” he said.
The tests many scientists use, such as those used to diagnose COVID-19 in people, home in on a piece of the viral RNA and amplify this target so that it can be detectable, Dr. Evans said. However, these tests do not determine whether there is any viable virus there. To do so, scientists need to take a sample collected from an area and put it into a cell culture, he said. If viable virus is present, it will infect the cells in the culture, whereas viral RNA, on its own, will not.
Dr. Evans said researchers in China, who conducted an environmental study in hospitals and in public places, were able to find viable virus only in highly contaminated areas – namely health care settings, such as in certain hospital bathrooms or change rooms where staff removed their personal protective equipment.
The risk of catching COVID-19 from a surface also depends not only the presence of viable virus, but on how much of it is deposited there. Dr. Evans said people tend to shed the greatest amount of virus particles from their upper respiratory tract within a day or two of developing symptoms. For those with mild disease, after eight or nine days of being sick, “the amount of virus they’re shedding that’s actually infectious is virtually zero,” he said.
Transmission through fomites also depends on many other variables, including the material upon which it is deposited. The virus is not able to survive as long on hard, nonporous materials such as stainless steel, where it is more exposed to the environment than, for example, on the palm of your hands and covered in respiratory secretions, he said.
High temperatures and high humidity seem to reduce its ability to establish an infection, though the relationship is not always clear-cut, he added. Moreover, ultraviolet light from the sun likely renders the virus inactive, which is why using outdoor playground equipment is probably not so risky, he said.
Given all these factors, Dr. Evans said it’s still worth investing in cleaning and disinfecting.
But, he said, “The problem with disinfecting protocols – and I’m all for them by way … – is that it’s really not addressing the major route of transmission, which is respiratory droplet transmission.”
Samira Mubareka, a virologist and infectious-disease specialist at Sunnybrook Health Sciences Centre in Toronto, said she had similar thoughts as Dr. Goldman about the limitations of the studies he discussed in The Lancet. However, she still personally wouldn’t be comfortable allowing children to play on playground equipment.
Dr. Mubareka said while there’s a general consensus that close, sustained contact with infected individuals leads to transmission, it’s hard to determine in those situations whether the virus is spread through contact with fomites or shared breathing zones.
Among households and nursing homes, where a lot of transmission occurs, “it’s hard to separate those two things. Both are co-exposures.”
Since there are so many variables that could affect whether one catches COVID-19 from fomites, including human behaviour – such as whether children touch their faces after contact with a shared surface – Dr. Mubareka said the risk will vary from one situation to another.
“It won’t be black and white. … In a lot of cases, that take home [message] is to really understand the situation that you’re in.”