Pneumonia facts. 1  Pneumonia is inflammation of the airspaces in the lungs, most commonly due to an infection. 2  Pneumonia may be caused by viruses, bacteria, or fungi. 3  The most common bacterial type that causes pneumonia is Streptococcus pneumoniae. 4  Signs and symptoms of pneumonia include. 5  fever, 6  chills, 7  cough, 8  shortness of breath, 9  fatigue. 10  Community-