Pneumonia is an inflammation of the lungs caused by bacteria, viruses, or chemical irritants.
It is a serious infection or inflammation in which the air sacs fill with pus and other liquid. The Streptococcus pneumoniae is the most common bacterium that causes bacterial pneumonia. It usually occurs when the body is weakened in some way, such as illness, malnutrition, old age, or impaired immunity, and the bacteria are able to work their way into the lungs. Early symptoms of viral pneumonia are the same as those of bacterial pneumonia, which may be followed by increasing breathlessness and a worsening of the cough. Viral pneumonias may make a person susceptible to bacterial pneumonia.