Photo: Ryan Remiorz, The canadian Press
In public buildings, such as shopping malls or office buildings, we must ensure that there is adequate ventilation.
This week, 239 scientists from 32 countries have published an article asking the world health Organization (WHO) to recognize the potential of air-borne transmission of the coronavirus. Interview with Raymond Tellier, a microbiologist of the McGill university health Centre, which is part of the signatories.
In what proportion do you estimate the share of the aerosol transmission ?
For the COVID,it is difficult to say. If I refer to the influenza, it is probably somewhere between 10 and 50 % of the cases where the aerosol plays a role. It depends of course of study, the environments, but it is roughly the order of magnitude. There is also something intriguing with the influenza. If you acquire by aerosols, you have more chance of having a severe disease. In reality, it is easy to understand : particles larger than 20 microns will not penetrate into the lower respiratory tract, whereas smaller particles will be able to go to the lungs and trigger an infection.Therefore, in the case of influenza, if it is just 10 % of the cases, but 10 % more severe, it is a route of transmission that is worth to be interrupted.
What this means for public health and for the people ?
The result, as expressed in our letter, is that it is necessary to first ensure, particularly in hospital environments, ventilation systems are adequate. So that there is sufficient air changes and that, if the air is recycled, it is treated by filtration or by exposure to ultraviolet light. The personal protective equipment shall be appropriate for the care of patients who have COVID, that is to say, that it is necessary to use masks N-95. A surgical mask offers incomplete protection against aerosols. In public buildings, such as shopping malls or office buildings, we must also ensure that there is adequate ventilation. Finally, it is also an additional reason to apply the mask to all.
Which study shows the more clearly that the air-borne transmission of the COVID-19 is real ?
The air has been fairly well demonstrated for certain outbreaks, such as an outbreak in a choir in Washington State and another in a restaurant in Wuhan. In addition, with molecular tests, we confirmed the presence of the virus in the air of hospital rooms in Wuhan and in the state of Nebraska. Through laboratory studies, we also know that, if you create aerosol-infected and to leave it in suspension in the air, a good amount of the virus remain infectious for several hours, even if the infectivity decreases exponentially in time. […]
Why do we say that the aerosols do not transmit SARS-CoV-2 : because the virus does not survive, or because the dose is not enough ?
There is a little bit of both. One of the objections canonical to be transmitted via aerosols, it is noted that there is no transmission, the long range of the COVID, unlike measles. The answer to this argument is multi-faceted. First of all, it depends on the amount of virus that is produced in the aerosol. It depends on the amount of virus required to initiate infection. It depends on the potential duration of infection of the viral particle. And it depends on the ventilation. […] In short, this is not because there is no transmission at long-range that there is no danger by aerosols.
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Why have you decided to sign this letter ?
This issue is important to me because I’ve worked for years in the context of the influenza virus. In the case of influenza, the public Health does not consider that transmission by aerosol is important, in spite of the fact that many of the publications, carried out over decades, show that it plays a role. The second reason is that it has been seen several times, during epidemics of SARS and respiratory syndrome in the Middle East, that these coronavirus emerging could form infectious aerosols. And therefore, there was every reason to believe that this would be the same thing with this new coronavirus.
The result of your output, WHO’s changed his position, recognizing that “emerging evidence” were going in the direction of a transmission aerial. How do you see the future ?
We are very encouraged by the response of the WHO, although his language remains pretty cautious. This is not an acceptance, without a doubt, but a recognition that the data seem to indicate that there are contexts where the air-borne transmission plays a role.
Obviously, a very difficult question that has not been solved is to know what proportion of infections is caused by aerosols, and how much by larger droplets, even if the dichotomy is not quite correct, because there is a continuum of particles. One thing is for certain, this proportion should vary from one environment to the other. If there is poor ventilation, it will promote contamination by aerosols. One can think of the humidity also. Enveloped viruses, such as influenza or COVID, survive much better in aerosol spray cans if the humidity is low, as is the case in heated homes during the winter, but also in the air-conditioned units during the summer.