The coronavirus that causes Covid-19 can adhere to stainless steel and plastic surfaces for up to four days, and to the outer layer of a face mask for a week, according to a study by researchers from the University of Hong Kong (HKU).

The team also found that common household disinfectants, including bleach, were effective in “killing” the virus.

The report, published in medical journal The 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.

“Sars-CoV-2 can be highly stable in a favourable environment, but it is also susceptible to standard disinfection methods,” said the researchers, who included, from HKU’s school of public health, Leo Poon Lit-man, head of the public health laboratory sciences division, and Malik Peiris, a clinical and public health virologist.

The researchers tested how long the virus could remain infectious at room temperature on various surfaces.

On printing and tissue paper it lasted less than three hours, while on treated wood and cloth – a standard cotton laboratory jacket – it disappeared by the second day.

On glass and banknotes the virus was still evident on the second day, but had gone by the fourth, while on stainless steel and plastic it was present for between four and seven days.

The researchers said that “strikingly” there was still a detectable level of infection on the outer layer of a surgical face mask after seven days.

“This is exactly why it is very important if you are wearing a surgical mask you don’t touch the outside of the mask,” Peiris said.
“Because you can contaminate your hands and if you touch your eyes you could be transferring the virus to your eyes.”

On all surfaces, the concentration of the virus reduced quite rapidly over time, the study said.

The researchers also 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.

A study by American researchers on the environmental stability of the coronavirus published last month in the scientific journal Nature also concluded that it could 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 last more than four hours on copper or 24 hours on cardboard.

The team included scientists from the National Institute of Allergy and Infectious Diseases and the US Centres for Disease Control and Prevention

.The findings from HKU add 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, 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,” he said.

People who were particularly concerned might prefer to leave non-perishable items in their shopping bags in the kitchen for a day before handling them, he said.

“That would reduce the viral titre [concentration] a lot. But the most important message is wash your hands.”