Empyema doesn’t occur on its own; it is a complication of other medical conditions. In order for empyema to occur, bacteria, fungi, or chemicals must get into your pleural space and cause inflammation, leading to the production of pus.
Lung infections, such as pneumonia, and lung abscess are two of the most common ways that bacteria get into your pleural space.
According to the medical journal Chest, there are two classes of empyema: simple and complex.