Airborne and Droplet Transmission

Many of the diseases spread by airborne or droplet transmission produce systemic illnesses which may include respiratory symptoms and skin rash. The difference between airborne and droplet transmission is in the size of the particles expelled. Droplet transmission occurs by droplets greater than five microns in diameter. The droplets are sprayed into the air, but usually fall short of three feet. Exposure does not generally occur beyond this range. Diseases spread by droplet transmission include influenza, pertussis, and mumps.

Aerosolized droplet nuclei smaller than five microns may remain in the air longer than larger droplets, increasing the range at and length of time during which people can be exposed. Diseases spread by airborne transmission include measles and tuberculosis.   Infections like influenza or the common cold can be passed either through respiratory secretions, or by touch contact from mucus membranes. The infective dose and the degree of exposure play a large role in the transmission of these diseases. The force with which particles are expelled also influences their communicability, such as with pertussis. Close contacts are more likely than others to become infected. In addition, host factors like nutrition status also play a large role in determining whether a contact can resist infection.
Image showing droplet spread from a typical sneeze
Chest x-ray of patient with advanced tuberculosis