Pneumonia is an infection usually caused by either bacteria or a virus. It involves the alveoli in one or both lungs filling with exudate, which interferes with 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, and in the elderly. Pneumonia can strike suddenly or gradually. According to the Lung Foundation of Australia, there are over 77,500 pneumonia hospitalisations in Australia each year, and the average length of stay rises with age – from 6 days for those under 65 to 13 days for those 65+. In 2012, there were 2,567 deaths due to influenza and pneumonia in Australia, with the median age at death 86 years for males and 90 years for females.