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15 July 2020
Updated on July 16, 2020 at 16h49
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Verification: the COVID-19 is transmitted by aerosol ?
Jean-François Cliche
The Sun
VERIFICATION / affirmation : “Initially it was believed that the new coronavirus has spread in droplets, which may be retained by a cover face. But is there new information that confirm that the virus is spread by aerosol ? If this is the case, then the masks craft will not be very efficient. So is it true that the COVID-19 can be transmitted by aerosol?”, request Marie-Pierre Lapointe, Quebec.
The facts
There are essentially three routes by which respiratory viruses can theoretically be transmitted. It can include droplets more or less “big” (some may have less than 1 mm in diameter, and can be imperceptible), which will either go directly to another person, or to deposit quickly onto a surface, generally within 2 meters of the person issuing it. These droplets can then, and this is the second way possible, be involuntarily affected finger by someone, who proceeds to infect then bringing his hands to his face. Note that the surfaces can also be contaminated by a patient who has secretions on the hands.
Or, third possibility, the virus is transmitted by droplets so fine that they put a lot of time before being deposited, remaining suspended in the air for 1 hour or more, and travelling over distances much larger than 2 meters. It is these micro-droplets are called aerosols. It is generally considered that a droplet must be less than 5 microns (or, if one prefers : a 200th of a millimetre) to behave like an aerosol, but we are dealing here with a continuum. According to this article published in 2006 in the medical journal Emerging Infectious Diseases, the small droplets of 100 microns (0.1 mm) in diameter, which is about 3 meters in the air takes about 10 seconds before reaching the ground. To 20 microns (0.02 mm), it takes 4 minutes, 17 minutes to 10 microns and not less than 62 minutes to 5 microns.
It goes without saying that transmission by aerosol makes a huge difference in an epidemic. The simple fact of finding themselves in a room where talking about an infected person can be enough to catch a disease that travel spray, so it takes a contact a lot more support for the microbes “droplet”.
In regards to the COVID-19, it seems to assume that it is spread by droplets (“big”) and by the surfaces. At least, almost nobody disputes that these are modes of transmission are important. The path of the aerosol, however, is much more controversial.
It is authentic experts believe that it is a pathway of infection significantly. More than 200 researchers have co-authored this month an open letter in the journal Clinical Infectious Diseases a trial in this sense. This has prompted the world health Organization to revise its position on the subject. While WHO was considered before this path as likely only the result of certain medical procedures (such as respiratory care), is known to produce a lot of aerosols, it is estimated now “possible” in other circumstances, in particular when groups remain a long time in enclosed spaces and poorly ventilated areas.
But between “possible path” and “way important” or “prominent”, there is a great not that not all of them are ready to step up. The current debate that is taking place in the medical community focuses on it. The evidence of transmission aerosol we have for the moment are often described as anecdotal, and not particularly clear by several observers.
For example, we have detected the genetic material of the COVID-19 in samples of air at several occasions, including in China, Singapore and Italy. On one side, it could actually mean that the virus travels in the form of aerosols. But on the other, it is not known if this genetic material belonged to a virus “living” and the infectious, or virus “dead” who can’t make the person sick.
One way around this problem is to examine cases of “super-spread”, where the aerosols are believed to have played an important role. But here you are, those as we know are rather ambiguous enough to be interpreted in a sense as in the other.
Stand : January 24, 10 persons belonging to three families were infected by the COVID-19 during the same evening in a restaurant in Guangzhou, China. For the chemist of the University of Colorado Jose-Luis Jimenez, an expert on aerosols, which is convinced that more than 50 % of the infections with the coronavirus pass by this way, it is necessary to do “contortions intellectual” to explain this episode without aerosol transmission, since 10 people were seated at three different tables, often back-to-back. But for the doctor, and blogger american David Gorski, this is not so convincing as this because the three tables were side-by-side, and that none of the servers nor 68 other customers present that night, who were not far away, has not been infected.
And the other known cases of super-spreading all suffer from a common problem : they are produced in confined spaces, among people who were relatively close to each other. In these conditions, it is difficult to tell if the virus has traveled by droplet or aerosol. If we had to deal with a case where the contagion would have arrived, for example, in an office tower between people who do not work on the same floor, we could probably exclude the droplets. But when it comes to people eating at tables nearby or who all sing in the same choir (to 30 cm from each other), it is not obvious.
In addition, read-on Monday in the Journal of the American Medical Association, several features of the COVID-19 are inconsistent with the idea that aerosols would be a channel of contagion important or predominant. Thus, the famous “R0” of the novel coronavirus is between 2 and 3, which means that a sick person will infect 2 or 3 others on average. It is much closer to the flu (around 1.5) which is transmitted mainly by droplets and by the surface, that the R0 of diseases that are known to travel in aerosol (measles, for example, has an R0 between 12 and 18).
And then, note the article in JAMA, the risk of transmission between people living under one roof varies between 10 and 40 %, and it falls to 7 % for close contact but less supported, such as sharing a meal. This seems too low for a virus that would be transmitted efficiently via aerosol.
Verdict
Not clear. There are studies and expert reports that clearly suggest that at least in some circumstances (long-past period in a poorly ventilated space), the COVID-19 is able to be spread by aerosol. But there are also a lot of data and expertise, which suggest that this should not be a route of transmission important. You need to wait until other studies seem to be before to be certain.
