In many practical situations, the transmission of the coronavirus by aerosols is not very efficient. But there are also more risky situations, for example in poorly ventilated rooms or when there are 'superspreaders'. This is the conclusion of a team of UvA physicists and medical researchers from Amsterdam UMC and the Cardiology Centres Netherlands.

The research was carried out by physicist Daniel Bonn and his research group (University of Amsterdam) in collaboration with medical researchers Aernout Somsen (CCN), Lia van der Hoek and Reinout Bem (Amsterdam UMC). The results were published this week in the professional journal Physics of Fluids.

The risk of microdroplets

An important way in which the coronavirus can be transmitted is by inhaling aerosols, droplets contaminated with the virus. Such droplets are released by speaking, coughing or sneezing. It is known that larger droplets, which also contain the largest numbers of viruses, quickly fall to the ground and therefore pose little risk if you wear a mouth mask and keep a sufficient distance. Smaller microdroplets, on the other hand, can float in the air for minutes. The extent to which these droplets play a role in the transmission of the coronavirus has therefore recently led to much discussion.

Speaking, coughing or sneezing

Using the very latest techniques for visualising these droplets and physical models, the scientists investigated exactly how long microdroplets released during speaking, coughing or sneezing remain suspended in the air. With this information, the role of aerosols in the transmission of the virus could be studied directly. The researchers found that in people with mild symptoms, aerosol particles are generally a rather inefficient way of transmitting the virus. However, in small and poorly ventilated rooms where there is constant talking, coughing and sneezing, the results show an increased risk of the virus being spread by microdroplets. Superspreader individuals also appear to produce almost twenty times more aerosols than normal individuals, thus also posing a greater riske.