Airborne transmission is possible for essentially all classes of microbes: viruses, bacteria, fungi and protozoans.
Any respiratory pathogen able to survive aerosolization and air transport is considered a potential cause of airborne disease.
Aerosols: Airborne particles, either solid or liquid, about 0.5 to 20 microns in diameter, that remain airborne for extended periods of time.
Droplets: >20 (usually 100+) microns in diameter; settle rapidly or evaporate to form droplet nuclei in the aerosol size range.