Table 1.

Traditional versus updated understanding of airborne transmission

	Traditional: droplet vs aerosol dichotomy	Updated: inhalation
Relative importance of droplets and aerosols	Droplets are thought to be responsible for most transmission of respiratory viruses; aerosols are important for certain pathogens like tuberculosis or measles.32	Both droplets and aerosols contribute to transmission, though short range aerosols are the most important vehicle for most respiratory viruses.33
Role of proximity	Most aerosol transmissions are thought to happen at longer distances.	Proximity is important for droplets and aerosols, with concentrations decreased by gravity and dilution for droplets and dilution for aerosols.
Role of masking	Surgical masking is sufficient for preventing droplet transmission; respirator/N95 masks are needed to prevent aerosol transmission.34	Surgical masks (especially when worn by source) provide some (but not complete) protection against aerosols.35 There is a theoretic benefit to a respirator/N95, although the incremental benefit has not been clearly demonstrated in clinical trials or real-world studies to date.
Role of ventilation	Not necessary for droplet spread; needed for aerosols or pathogens primarily transmitted via droplets when index cases undergo aerosol generating procedures.	An important tool that can be used to decrease risk of most respiratory pathogens through dilutional mechanism.