Pneumococcal pneumonia is a common but serious infection and inflammation of the lungs. It is caused by the bacterium Streptococcus pneumoniae, in which is the cause of many human diseases, including pneumonia.

Although the bacteria can normally be found in the nose and throat of healthy individuals, it can grow and cause infection when the immune system is weakened. Infection usually begins with the upper respiratory tract and then travels into the lungs. Pneumonia occurs when the bacteria find their way deep into the lungs, to the area called the alveoli, or air sacs. This is the functional part of the lungs where oxygen is absorbed into the blood. Once in the alveoli, Streptococcus pneumoniae begin to grow and multiply. White blood cells and immune proteins from the blood also accumulate at the site of infection in the alveoli. As the alveoli fill with these substances...