The diseases which spread through air are known as air borne diseases. Airborne diseases are commonly spread by sneezing and coughing, and can sometimes also spread by touching a common thing like a pen, keyboard or by handshake. It might be possible that a person just covered his mouth while sneezing or coughing, the microbes are transmitted to his hands and when he touches different things he might infect them and in turn infect a disease free person.