We can continue to obsessively disinfect surfaces, pretending to have solved the problem; or, we can take advantage of this time of truce due to vaccines and the warm season to improve ventilation in closed spaces. The SARS-CoV-2 coronavirus is – we should have learned by now – an airborne pathogen, and its preferred means of transport are exhaled droplets when we talk.
Speaking without a mask in poorly ventilated closed places is the best way to transmit or contract CoViD-19: this is confirmed by a review of all the studies published so far on the subject, which came to this conclusion after comparing the risk posed by activities such as conversing, breathing, coughing and sneezing, singing.
From least to most dangerous. All respiratory aerosols begin their “journey” as thicker droplets, droplets whose liquid component evaporates almost completely in a short time. The ability of the residual gaseous part to remain suspended in the air depends on the initial size of the droplets emitted: even if the thicker droplets, spittle for example when we cast a “P”, can carry more viral particles, they are however produced in smaller quantities, and fall back to the ground quickly, posing a low risk of transmission.
More worrying are the fine aerosols capable of descending deep into the lower respiratory tract, and causing severe covid from there. Given their small volume, the amount of viruses they can carry is limited: but in closed and crowded environments, with inadequate ventilation, they can still accumulate and increase the risk of infection.
Between these two extremes there is the most significant portion of aerosol emitted when we speak: that of intermediate size, capable of remaining suspended from the ground for several minutes and being transported to the opposite side of the room by the internal recirculation of the air. The abundance of these particles, combined with the high viral load of certain positive and pre-symptomatic people, makes talking indoors absolutely the privileged way of transmission of covid. In fact, this activity brings together a series of concomitant and unfortunate conditions, such as the right size and abundance of droplets, the frequency of their emission and their permanence in the air.
What remains to be done. In addition to completing the vaccination campaign, the scientists write, we should emphasize the importance of using masks when we talk indoors (for example, if we talk while others eat, and necessarily are unprotected); it is also necessary to ensure ventilation measures capable of removing stagnant aerosols from the room.
Finally, a useful reminder: the masks will not be perfect, but if – remember the researchers – that of a positive and unaware individual also lets 25% of respiratory droplets pass, the risk of inhaling the virus in those close to him would still be reduced by four times. And when people exposed to the virus also wear a face mask with 50% filtering efficiency, the probability of infection is reduced by 8 times compared to a dialogue without face masks. If everyone did their part, the spread of covid would be definitively cut down.