It was one of the great unknowns of the new coronavirus Covid-19, which appeared in China at the end of 2019. According to a study, the results of which were published on Tuesday by the New England Journal of Medicine (NEJM), the latter can actually survive for several hours outside the human body, on various surfaces or even in the air.
The authors of this work, scientists from the Centers for Disease Control and Prevention (CDC), the University of California at Los Angeles and Princeton, found that the virus responsible for the current epidemic had a level of viability. in the open air comparable to that of the coronavirus causing SARS (severe acute respiratory syndrome).
This could mean that the magnitude of the Covid-19 pandemic – far greater than that of SARS in 2002-2003 – is linked to the fact that it is much more easily transmitted from an asymptomatic (“healthy”) carrier to a other.
Results subject to criticism?
During the experiments, it could also be shown that the new coronavirus was detectable for up to two to three days on plastic or stainless steel surfaces, and up to 24 hours on cardboard.
The researchers also used a nebulizer to spread the virus to ambient air. Using this technique, they found traces of the virus in the form of an aerosol – that is, particles suspended in the air – for three hours.
Put online for professionals before being examined by a reading committee, the study had however drawn criticism, experts judging that the use of a nebulizer did not simulate cough or sneezing well. ‘a patient and risked artificially increasing the extent of airborne contamination.
Shadow areas remain
The virus is mainly transmitted by micro-droplets expelled by patients when they cough or sneeze, and in this form (different from an aerosol) it is only viable for a few seconds.
Similar tests with the SARS coronavirus have resulted in equivalent viability outside the human body.
This does not explain why the Covid-19 pandemic affects nearly 200,000 people, with some 8,000 deaths, while SARS infected only 8,000 patients and killed 800.
The epidemiological differences “probably stem from other factors, such as a higher viral load in the upper respiratory tract” and the ability of patients without symptoms to transmit the new coronavirus, say the study authors.
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