Flowing droplets: a perspective on the transmission of respiratory infectious diseases

João M. Miranda
CEFT - Transport Phenomena Research Center, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal 

Most respiratory infectious diseases are transmitted through respiratory droplets by expelling events such as talking, singing, coughing or sneezing. The agents of the disease (bacteria or virus) are transported inside the droplets and, when reaching the respiratory system of another individual, can initiate a new infection. So, the dynamics of the droplets transport in air, after their release by the infected person, is crucial to understand and prevent disease transmission.

The following aspects of the droplet transport are addressed: size distribution of the droplets released by expelling events, trajectories and distance reached by droplets, effect of buoyancy, humidity and temperature on particle trajectory and residence time. The main implications for transmission control are analyzed, with emphasis on methods to reduce SARS-COV-2 transmission. The following methods are analyzed: social distancing, individual protection equipment and indoor control of humidity and temperature. Finally, implications for mask design are addressed. 

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