Washington (AFP)
A group of 239 international scientists on Monday called on world health authorities and in particular the World Health Organization (WHO) to recognize that the new coronavirus can spread in the air far beyond two meters and therefore recommend vigorous ventilation of indoor public spaces.
Their letter is directly aimed at the UN organization, already criticized for having delayed recommending the masks, and here accused of refusing to see the accumulation of indications of an air propagation of the virus which killed more than 500,000 people in the world in six months.
WHO and other health agencies believe that the coronavirus is mainly transmitted by droplets sprayed by coughing, sneezing and speech directly on the face of people nearby, and possibly by surfaces where these postlets land and are then recovered by the hands of healthy people. These droplets are heavy and fall within a perimeter of about one meter.
Hence the priority given in the health instructions to physical distancing, washing hands and wearing a mask.
But studies on SARS-CoV-2 and other respiratory viruses have shown that viral particles are also present in microscopic droplets (less than 5 microns in diameter) in the air exhaled by an infected person; lighter, they can stay suspended indoors, potentially for hours, and be inspired by other people. These coronavirus particles have never been proven to be viable and can cause infection; but the clues are piling up.
"We call on the medical community and the competent national and international organizations to recognize the potential of aerial transmission of Covid-19", write in the journal Clinical Infectious Diseases of Oxford two scientists, Lidia Morawska of the University of Queensland (Australia) and Donald Milton of the University of Maryland, in an article signed by 237 other experts.
"There is a significant potential for the risk of inhalation of viruses contained in microscopic respiratory droplets (microdroplets) at short and medium distances (up to several meters, on the order of the scale of a room), and we advocate the use of preventive measures to prevent this route of airborne transmission, "they continue.
- Renew the air -
There is no scientific consensus that this airway plays a role in contagions: but Julian Tang, one of the signatories, from the University of Leicester, replies that the WHO has not proved the opposite : "The absence of proof is not proof of absence."
At the time of deconfinement, it is urgent, experts argue, to better ventilate workplaces, schools, hospitals and retirement homes, and to install infection control tools such as sophisticated air filters and special ultraviolet rays that kill microbes in the air ducts.
Authorities in the United States and Europe are ahead of the WHO. "Increase the circulation of outside air as much as possible," advise the Centers for Disease Prevention and Control (CDC).
The European CDC explained on June 22 that air conditioning could dilute the virus in the air and remove it, but it could have the opposite effect if the ventilation system did not renew the air and recirculated it to the same pieces.
A famous example is that of a cluster started in a Canton restaurant in January: a symptomless person contaminated customers of two neighboring tables, without contact; the air conditioner likely caused the virus to fly from one table to another.
Other cases of super-contagions, in a Chinese coach and in an American choir, also accredit the air strip.
"Transmission by air of SARS-CoV-2 is not universally accepted; but our collective opinion is that there is enough evidence to apply the precautionary principle," say the scientists.
WHO distinguishes between air-borne viruses, such as measles and tuberculosis, and others, but "it's not a dichotomy problem," another signatory, the professor, told AFP. Caroline Duchaine, director of the bioaerosol laboratory at the University of Laval in Quebec.
"We make a mistake if we make an opposition between transmission by viruses like measles and by Covid-19," she said.
© 2020 AFP