Pneumonia is an infection in one or both lungs that can cause mild to severe illness in people of all ages. It causes inflammation and can lead to the air sacs (alveoli) in the lungs filling up with fluid. This can make it hard for oxygen to reach the blood stream and cause wheezing or difficulty breathing.

Pneumonia is caused by various organisms like bacteria, viruses or fungi. A common cause of bacterial pneumonia is due to a bacteria called Streptococcus pneumoniae, also known as pneumococcus.