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Coronavirus-COVID-19: survival in the air we exhale (aerosol)
Air samples or infected surfaces are observed to measure the permanence and spread of the virus.
With special techniques (Focus forming assay FFA) the presence of infectious viruses is measured over time, at regular intervals. The concentration is expressed in TCID50.
Techniques for measuring the concentration of the active virus The technique used only detects the presence of viruses that can cause an infection. It does not detect the presence of ineffective viruses.
The air we exhale contains different particles dissolved and/or sprayed. For this reason it is called aerosol (which means solution in the air)
Exhaled air is an aerosol containing endogenously generated droplets.The term aerosol means solution in the air, that is, air in which liquid or solid particles are dissolved or suspended.
To carry out the tests you can use the air exhaled by people or artificially create a similar solution, also called aerosols.
Try exhaling on a cold surface, like a glass removed from the fridge. You will see that very small droplets of steam are deposited on the surface. This is the moisture we emit, melted in our breath, and therefore definable as aerosols: solution in the air.
For this reason many people thought that this trial referred to the case where an infected person performs aerosol therapy. Absolutely absurd and wrong, the experimentation concerns the air exhaled by people, which is an aerosol as it contains moisture and other particles.
The trial uses the aerosol technique to accurately and consistently create air in the laboratory similar to that emitted by a person infected with the virus.
Coronavirus-COVID-19: survival of the virus in the exhaled air. After three hours, the concentration decreased by 10^0.8, equivalent to 6.3 times.Staying of the virus in the exhaled air (called aerosol)
On the right you can see the virus's survival tests in the exhaled air.
Coronavirus-COVID-19 (in red) is compared to the SARS virus, in purple.
The scale on the left indicates the concentration of the virus. The scale below shows the hours.
We see that for Coronavirus-COVID-19 we initially have a concentration of 10^3.5 (about 3162 TCID50)
After three hours this concentration drops to 10^2.7 (about 500 TCID50) so about 6.3 times less.
The limit under which the virus is not detectable with this method is about 10^1 (about 10 TCID50)
Significate charts and considerations
These graphs give a measure of the possibility of contagion over time, which is the probability of the virus spreading.
Mortality is affected by the effects of the virus. For example, the flu of 2018-2019 infected about 60 times more people than Coronavirus-COVID-19, but with a much lower mortality.
That's what that means.
If we imagine a closed environment, if an infected person passes, it releases air with a concentration of the virus of about 3162 TCID50.
If after three hours we enter the room the concentration of the virus could be about 500 TCID50, then nothing but nothing.
However, it must also be considered that the air emitted by the person disperses into the room, and if we are outdoors even a slight wind can greatly decrease the concentration of the virus.
Eeee it is clear that we can find a dangerous concentration of the virus: Anywhere in the previous hours, there were people who might be infected.
- The more people who are present or have passed through the environment, the more likely they are to find a high contraction of the virus.
Also: Maintaining the interpersonal distance of one meter, which some governments indicate in two meters, decreases the probability of contagion, but gives us no guarantee of not being infected.
To date, no infections have been proven by inhalation of exhaled air after hours, but we know with confidence that this air may contain consistent concentrations of the virus.
Precautionary measures, therefore, it is appropriate to
- Often area the premises, three or four times a day
- avoid the absolute way that forced ventilation systems perform an air recirculation. Possibly call a specialist technician for guidance on how to adjust your system.
- avoid as much as possible access to outdoor premises or areas where in the previous hours people who may be infected have stayed or transited.
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