Pneumonia
Pneumonia is a type of lung infection, caused by a virus or bacteria. The lungs are filled with thousands of tubes, called bronchi, which end in smaller sacs called alveoli. Each one has a fine mesh of capillaries. This is where oxygen is added to the blood and carbon dioxide removed. If a person has pneumonia, the alveoli in one or both lungs fill with pus and fluids (exudate), which hinders the gas exchange. This is sometimes known as 'consolidation and collapse of the lung'.
Anyone of any age can contract pneumonia, but it tends to be common in children aged four years and under. Pneumonia can strike suddenly or gradually. With appropriate treatment, one can expect to get better in around one week to 10 days.