Infectious diseases can spread from one person to another by aerosol droplets. The spread of Tuberculosis (TB), for example, occurs when an otherwise healthy individual inhales a sufficient number of tubercle bacilli that are expelled by a patient infected with pulmonary TB. Thus it spreads rapidly to the healthy persons. To avoid this hospitals provide special room to treat this patients..http://www.airtech.com.sg/Infections_Disease_Treatment_Room.html