The coronavirus can still be found on the outer layer of a face mask after seven days, according to a study by researchers from the University of Hong Kong (HKU).

The report was published in medical journal The Lancet on Thursday, April 2.

The stability of SARS-CoV-2, as the coronavirus is formally called, has already been known, as it can adhere to stainless steel and plastic surfaces for up to four days.

But the Hong Kong team also found that common household disinfectants, including bleach, were effective in "killing" the virus.

Different surfaces, different duration

"SARS-CoV-2 can be highly stable in a favourable environment, but it is also susceptible to standard disinfection methods," said the researchers.

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

On printing and tissue paper it lasted less than three hours.

On treated wood and cloth, such as a standard cotton laboratory jacket, it had disappeared by the second day.

On glass and banknotes the virus was still evident on the second day, but had gone by the fourth.

On stainless steel and plastic it was present for between four and seven days.

There was still a detectable level of infection on the outer layer of a surgical face mask after seven days, the researchers found.

This is exactly why it is very important if you are wearing a surgical mask that you don't touch the outside of the mask, the researcher said.

"Because you can contaminate your hands and if you touch your eyes you could be transferring the virus to your eyes."

Lab vs real-life

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

However, the researchers said the results did "not necessarily reflect the potential to pick up the virus from casual contact".

This was so as the presence of the virus in the study was detected by laboratory tools, not fingers and hands.

Hand-washing remains at the top of the list of must-dos, the researcher said, as 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.

The researchers included 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.

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