Pneumonia means infection of the lungs. The majority of pneumonias come from bacteria (bacterial pneumonia) and around ten percent
result from other microorganisms, including viruses and fungi. Contrary
to some common misperceptions, going outside with wet hair or leaving
your house without a jacket does not cause pneumonia. The majority
of pneumonias result from bacteria normally living in our mouth
and nose, which inadvertently pass down the trachea (windpipe) into
the lungs. Once the bacteria reach the lungs, they proliferate and
cause fever, cough and chest pain.
Some pneumonias may be transmitted from person to person through
respiratory droplets. A small percentage also comes from birds living
in the house (psitacosis), sheep (Q fever), or wild animals (tularemia).