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.
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