The coronavirus that causes Covid-19 can adhere to the outer layer of a face mask for a week, according to a study by researchers from the University of Hong Kong.
"This is exactly why it is very important if you are wearing a surgical mask you don't touch the outside of the mask," said Malik Peiris, a clinical and public health virologist at the University of Hong Kong and a member of the research team.
"Because you can contaminate your hands and if you touch your eyes you could be transferring the virus to your eyes."
The report, published in the medical journal Lancet on Thursday, adds to a growing body of research about the stability of SARS-CoV-2 " as the coronavirus is formally known " and what can be done to prevent its transmission.
Common household disinfectants, including bleach, were effective in "killing" the virus, the report said.
"Sars-CoV-2 can be highly stable in a favorable environment, but it is also susceptible to standard disinfection methods," said the researchers, who included Leo Poon Lit-man at the school of public health at the University of Hong Kong.
The virus can also stick on stainless steel and plastic surfaces for up to four days, the researchers said.
The researchers said that the results did "not necessarily reflect the potential to pick up the virus from casual contact," as the presence of the virus in the study was detected by laboratory tools, not fingers and hands as would be the case in everyday life.
The researchers tested how long the virus could remain infectious at room temperature on a variety of surfaces.
On printing and tissue paper it lasted less than three hours. The virus disappeared by the second day on treated wood and cloth " a standard cotton laboratory jacket.
The virus was still evident on glass and banknotes on the second day, but had gone by the fourth. On stainless steel and plastic it was present for between four and seven days.
On all surfaces, the concentration of the virus reduced quite rapidly over time, the study said.
A study by American researchers on the environmental stability of the coronavirus published last month in the scientific journal Nature also concluded that it can remain infectious on some surfaces for days.
They found the virus was present on plastic and steel for up to 72 hours but did not survive for more than four hours on copper and 24 hours on cardboard.
The team included scientists from the National Institute of Allergy and Infectious Diseases and the US Centers for Disease Control and Prevention.
The findings from the University of Hong Kong added to the conversation about public health and hygiene, and what kinds of precautions people should take when bringing items like groceries into their homes.
Hand washing remains at the top of the list for Poon, one of the researchers, who said it was theoretically possible for tins of food to carry enough live virus to cause an infection, but that the exact risk had yet to be established.
"If you want to protect yourself just maintain good hygiene, wash your hands often and try not to touch your face, your mouth or nose without cleaning first," Poon said.
He added that people could leave non-perishable items in their shopping bags in the kitchen for a day before handling them.
"That would reduce the viral (concentration) a lot. But the most important message is to wash your hands."
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