Coloured 3D computed tomography (CT) scan of the chest of a patient with pneumonia affecting the right lung (left). Pneumonia is most commonly caused by the bacteria Streptococcus pneumoniae. The pathogen is inhaled into a lung segment, or lobe, where it causes the alveoli (air sacs) to become blocked with pus. Symptoms include fever and chills, a cough with rusty-coloured or pus-like sputum and chest pain. Treatment is with antibiotics.