Since most forms of both viral and bacterial pneumonia are contagious, the disease exits the contagious phase when it is successfully contained in a hospital environment or fully treated by means of antibiotics and other methods.
A Cough, A Handshake
The main way someone with an early onset of pneumonia can pass it on to another person is by coughing. Tiny droplets from the person's mouth can propel onto the face or body of another person, who then ingests the microscopic fragments and incubates them.
Much like the flue and the common cold, the other main way people can pass on pneumonia is through direct, physical stranger contact. Typically, the way most people come into contact with an individual sufferer, without realizing it, is by shaking their hand.
In fact, it's important to remember that pneumonia is essentially just a difference receptacle-form of the same viruses that causes the common cold or the flu. In other words, if the same sorts of bacteria or viruses that are passed by mouth and hand stop at the throat, the receiving person gets a cold or the flu. But if those bacteria continue on to infiltrate the lung(s), it can turn into pneumonia.
Thirty Years of AIDS
It was in 1981 that the U.S. Centers for Disease Controls first identified a devastating form of pneumonia being passed around the highly connected world of gay men. It is an often forgotten fact of the still ongoing epidemic that many of those who got the HIV-AIDS virus went on to then die from a case of related pneumonia.
The official name of this strain is pneumocystis pneumonia, or PCP. The fungal bacteria at the root of this strain, pneumocystis jiroveci, is actually very common, with most children exposed to it by the time they reach the age of three-four. However, if a person's immune system is compromised, as in the case of AIDS, this very common agent can wreak havoc.