A study by researchers at the University of Hong Kong indicates that the coronavirus can adhere to stainless steel and plastic surfaces for up to four days, and to the outer layer of a face mask for up to a week.

The research, published in the scientific journal ‘The Lancet‘, also concludes that common household disinfectants, including chlorine, are effective in “killing” the virus. “Covid-19 may be highly stable in a favourable environment, but it is also susceptible to standard disinfection methods,” the researchers say in statements cited by the South China Morning Post.

In their research, the scientists tested how long the virus could remain at room temperature on various surfaces. On printing paper and tissue paper it lasted less than three hours, while on wood and treated fabrics, such as a standard cotton lab jacket, it disappeared on the second day. In the glass and in the banknotes the virus had still disappeared to the room, while in stainless steel and plastic it was present for between four and seven days.

Hygiene, the best measure

“Surprisingly,” the researchers found that there was still a detectable level of infection in the outer layer of a surgical face mask after seven days, so “it is very important that if you wear a surgical mask you do not touch the outside of it. “explains Malik Peiris, clinical and public health virologist at the University of Hong Kong. “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 decreased quite rapidly over time, according to the study. The researchers clarify, however, that the results “did not necessarily reflect the potential to collect the virus by casual contact,” since the presence of the virus in the study was detected by laboratory tools, and not by fingers and hands as would be the case in everyday life.

“It is very important that if you use a surgical mask you do not touch the outside of it because you can contaminate your hands”

Regarding what kind of precautions to take, Leo L. M. Poon, head of the science division of the public health laboratory at the University of Hong Kong and main author of the study, continues to insist on the importance of hygiene: “If you want to protect yourself, you just have to maintain good hygiene, wash your hands often and try not to touch your face, mouth or nose without cleaning yourself first.”

This research joins a study by American researchers on the environmental stability of the coronavirus, published a few weeks ago, which also concluded that the coronavirus could remain infectious on some surfaces for days. They found that the virus was present in plastic and steel for up to 72 hours, but did not last more than four hours in copper or 24 hours in cardboard. This residence time depends on factors such as temperature and the type of surface.

For example, with a temperature around 37 degrees, always according to these researchers, it can survive for two or three days in glass, cloth, metal, plastic or paper. In addition, the same study, done on infections in Hunan province (China), spoke of the real separation between people should be about four meters, contradicting the advice of health authorities around the world that people should stay separated to a “safe distance” of one to two meters.