Source avec lien : Proceedings of the National Academy of Sciences, 119(32). 10.1073/pnas.2204593119
La transmission par voie aérienne se produit par le transport de virus par les gouttelettes après l’expulsion d’un aérosol par un hôte infecté. L’efficacité de la transmission résulte de l’interaction entre la survie du virus dans la gouttelette qui sèche et le temps de suspension de la gouttelette dans l’air, contrôlé par le couplage entre l’évaporation de l’eau et la sédimentation de la gouttelette. En outre, les gouttelettes sont constituées d’un fluide respiratoire et présentent donc une composition complexe composée d’eau et de solutés non volatils. Ici, nous quantifions l’impact de cette composition complexe sur les différents phénomènes qui sous-tendent la transmission.
Airborne transmission occurs through droplet-mediated transport of viruses following the expulsion of an aerosol by an infected host. Transmission efficiency results from the interplay between virus survival in the drying droplet and droplet suspension time in the air, controlled by the coupling between water evaporation and droplet sedimentation. Furthermore, droplets are made of a respiratory fluid and thus, display a complex composition consisting of water and nonvolatile solutes. Here, we quantify the impact of this complex composition on the different phenomena underlying transmission. Solutes lead to a nonideal thermodynamic behavior, which sets an equilibrium droplet size that is independent of relative humidity. In contrast, solutes do not significantly hinder transport due to their low initial concentration. Realistic suspension times are computed and increase with increasing relative humidity or decreasing temperature. By uncoupling drying and suspended stages, we observe that enveloped viruses may remain infectious for hours in dried droplets. However, their infectivity decreases with increasing relative humidity or temperature after dozens of minutes. Examining expelled droplet size distributions in the light of these results leads to distinguishing two aerosols. Most droplets measure between 0 and 40 µm and compose an aerosol that remains suspended for hours. Its transmission efficiency is controlled by infectivity, which decreases with increasing humidity and temperature. Larger droplets form an aerosol that only remains suspended for minutes but corresponds to a much larger volume and thus, viral load. Its transmission efficiency is controlled by droplet suspension time, which decreases with increasing humidity and decreasing temperature.