Acute pleuritis, pericarditis and peritonitis are usually the result of a bacterial infection. Bacterial infection of the pleura occurs in the setting of pneumonia, secondarily involving the overlying pleura and resulting in a pleuric empyema. Acute infection of the peritoneal cavity is often secondary to inflammation of or injury to the bowel, as in bacterial peritonitis.
The fluid is a creamy pale yellow (purulent) and often foul-smelling. Cytologic preparations are highly cellular and composed almost exclusively of polymorphonuclear lymphocytes. Bacteria are demonstrated with special stains in some cases.
Malignant cells must be looked for carefully because acute infection may be a complication of metastatic malignancy.