The spread of disease depends on the ability of the infecting organism to survive outside its source. A source may be an infected person, an animal, an insect or even an inert object. Transmission also depends on the ability of the infecting organism to move from one place to another. Simply stated, an infected person comes into contact with a noninfected person and transmits the disease. Contact transmission can be either direct or indirect.
Direct transmission involves direct physical contact between two people.
A person may touch the weeping lesions of chickenpox, for example, and become infected. Direct transmission also involves droplet contact, where sneezing, coughing or talking contaminates the air with droplets. Cold and flu viruses are most commonly spread by droplet contact. Even with droplet contact, the contact must be direct, since droplets generally do not travel more than 12 feet from the source. Indirect transmission occurs when an infected person spreads the infection to an inanimate object, and a noninfected person touches or otherwise comes into contact with the infected object.