It is preceded by bronchial infection and is commonest in children (measles and whooping cough) and the elderly (chronic bronchitis and hypostatic pneumonia in debilitated patients in bed).

• 发病之前有支气管感染，这在儿童(麻疹及百日咳)及老年人(慢性支气管炎及卧床不起者的体位性肺炎)最常见。