Pneumonia may be caused by a variety of infectious agents: bacteria, viruses, rickettsias, and fungi. In addition, the disorder may be a primary one or may complicate preexisting pulmonary or systemic disease of an infectious or noninfectious nature. Essential, therefore, to the optimum management of pneumonia is knowledge of the etiological agent and of the pathogenesis of the illness to be treated.
Before treatment is begun, data derived from a complete history and physical examination of the patient should be at hand. In addition to the routine examination of the blood and urine, other laboratory studies, including posteroanterior and lateral roentgenograms of the chest and a culture of the blood and the sputum, should be performed. A study of the sputum is of especial importance, for, when pneumonia is of bacterial or fungal origin, it provides the most ready means of establishing the etiological agent. Sputum should be