Viruses, bacteria and other microorganisms are transmitted through tiny droplets of water in the air, known as aerosols.
They can live there for a long time and transfer from host to host.
This risk is particularly high in rooms with many people, such as waiting rooms, offices, gyms or school classrooms.
In general, the situation worsens because these rooms are not well ventilated or have no central ventilation.
Especially in winter, ventilation is also unpleasant: ideal conditions for viruses.