ABSTRACT
I. Introduction The last two decades have witnessed a major evolution in the classification of pneumonia. Traditionally, clinicians have classified pneumonia by clinical characteristics, dividing them into “acute” and “chronic” pneumonias. The term acute was linked to the presence of symptoms of less than three weeks’ duration and was indicative customarily of an infectious etiology. Chronic pneumonias tended to be either noninfectious, mycobacterial, fungal, or related to opportunistic infections. With the creation of subspecialty services and introduction of life-saving technologies (i.e., mechanical ventilation), the classification of pneumonia has shifted to a new scheme that revolves around the patient’s underlying risk factors. The advantage of this classification scheme over previous systems is that it can help guide the selection of appropriate initial treatments even before the microbiologic cause of the pneumonia is known.
