Transmission Mechanisms

Droplets – Particles larger than 5 – 10 micrometers in diameter, projected by the infected when breathing, talking or coughing and coming into contact with the eyes, mouth or nose of the people around. These droplets precipitate on the ground quickly.

Aerosols – Particles smaller than 5 micrometers in diameter, projected by the infected and that can be inhaled by people nearby. These particles can remain in the air for long periods of time (about 3 hours in suspension). These particles move with the movement of the air and can reach several meters. This is a more unexpected form of transmission because people can be contaminated even in the absence of other people (e.g. in an elevator), even while keeping the safety distance of 2 meters or wearing a mask.

For example in a meeting room, if there is an infected person, even if wearing a mask, this will lead to an increasing viral load. If the meeting lasts for hours, this viral load may be enough to infect the other participants even if everyone wears a mask. On a car trip, this possibility will be much greater because the air volume in a car is low.

Surfaces – contaminated with viral particles. In this case, people touching such surfaces and putting their hand to their eyes, mouth or nose are at risk of becoming infected. The most normal contact will be via the hands, but it can be via the mouth or nose, such as when putting on a shirt during a fitting. In this case, the infected person who has tried on the clothes before, may have deposited viral particles on the clothes (for example, the collar of the shirt) by the simple fact of breathing or even via secretions (saliva).

See WHO (World Health Organization)

Other respiratory viruses

The routes of transmission of respiratory viruses include direct contact, contaminated breaths, and airborne droplets of secretion. The viruses most commonly involved in respiratory infections are rhinovirus, respiratory syncytial virus (RSV), coronavirus, adenovirus, parainfluenza, and influenza. Rhinovirus and respiratory syncytial virus (RSV) are spread in part by direct hand contact with contaminated skin and environmental surfaces, followed by self-inoculation of the virus through the nose or eyes. Others, such as influenza virus, measles virus, and varicella zoster virus, can spread over longer distances through small aerosol particles (mean diameter < 5 µm), but even then direct contact, breathers, and large particles are still important in transmission. Most respiratory viruses can spread via aerosols of large particles (> 5 µm) over short distances (< 1 m). Transmission of respiratory viruses can be amplified by exposure time, close contact, grouping of people, family size, and lack of pre-existing immunity. Infectivity usually precedes the onset of symptoms.