Coronavirus: what is the risk of contagion from a contaminated surface?

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Contaminated surfaces are not the main way of transmitting the new coronavirus. And although it can happen to get infected, this transmission really requires a long chain of unfortunate events and rare combinations

(photo: Lino Mirgeler / picture alliance via Getty Images)

Disposable gloves and rivers of disinfectants. During the new pandemic coronavirus, one of the biggest concerns, besides having to keep the social distancing, was to be able to get infected even just by touching them surfaces contaminated by the virus. Like the shopping bag or a door handle. Although, in fact, the main one transmission mode of the new coronavirus, as has been reiterated several times during the pandemic, occurs through the saliva droplets that infected people emit by speaking, sneezing and coughing, over and over again the possibility has been highlighted that even just touching contaminated surfaces the virus could be contracted.

But, what is really the risk of being infected just by touching a contaminated surface? Only a few days ago, in combination with the reopening of commercial and production activities, the Ministry of Health has published a table in which the residence times of the coronavirus (or rather traces of viral rna, which therefore does not mean that the virus is viable and infectious) on different surfaces. For example, we read in the table, the infecting viral particles were detected up to half an hour on the printing paper, one day on the fabric and wood, two days on the banknotes and glass and up to four days on the plastic and surgical masks (the inner layer).

Also, according to a recent release from the Americans Centers for Disease Control and Prevention (Cdc) indirect contact from a contaminated surface, which experts call transmission of fomites (by fomitis is meant an object that if exposed to pathogenic microorganisms can transfer an infectious disease to a new host), there remains a potential risk for the transmission of Covid-19. “Based on data from coronavirus laboratory studies and what we know about respiratory diseases similar, it may be possible for a person to contract the COVID-19 touching a contaminated surface or object, and then touching his mouth, nose or eyes “, the experts of the Cdc write. “But that’s not the main way the virus spreads.”

The answer to the initial question, therefore, is yes (at least in theory) and it is precisely for this reason that it is essential to wash your hands frequently with water and soap and avoid touching your face. “What they are saying is that surfaces, like door handles or elevator buttons, are not the main engine of the Covid-19”explained to New York Times Erin Bromage, immunologist from the University of Massachusetts. “But it’s still a bad idea to touch your face. If someone who is contagious drinks from a glass and then touches it near the edge, then passing the same hand over his eyes or mouth, he can get sick “.

Infecting yourself by touching a contaminated surface requires, in fact, a long chain of events. “There is a long chain of events that should occur for someone to become infected through contact with food, mail, takeaway containers or other surfaces”, commented to the New York Times Julia Marcus, epidemiologist at Harvard Medical School. “The last step of this chain is to touch your eyes, nose or mouth with your contaminated hand. This means that the best way to make sure the chain is broken is to wash your hands. “

Although many experiments have shown that viral particles they can spread on surfaces, to be infected they must survive long enough and in a dose sufficient to be infectious. Indeed, as it suggests Eugene M. Chudnovsky of the City University of New York, surfaces are not a particularly effective medium for viral transmission. With flu, for example, millions of copies of the virus are needed to infect a person through contact between a surface and the nose, while only a few thousand are needed to infect a person when the flu virus enters the air in lungs.

The bottom line, therefore, is that the best way to protect us from coronavirus there remains that of social distancing, frequent washing of hands and wearing masks. He also expressed himself in this regard Donato Greco, epidemiologist and WHO consultant, according to which the rules imposed by the government for the reopening of the activities are all useless. “The only effective anti-infection measures are, and remain, three: social distancing, the use of masks and hand washing”, explained the expert in an interview given to theAdnkronos. Then focusing on the (very minimal) chances of getting infected by touching them surfaces, Greco claimed that SARS-CoV-2 is a respiratory transmission virus and getting infected by collecting the virus from a surface requires a sequence of unlikely, excessive, unfortunate, rare combinations “.

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