ABSTRACT
Severe community-acquired pneumoniae (CAP) can present as mild, moderate, or severe pneumonia. Patients with severe CAP require hospital admission and usually are admitted to the critical care unit (CCU). Patients with severe CAP in the CCU are those with compromised respiratory function requiring ventilatory support. The clinical presentation of severe CAP occurs in both normal and compromised hosts. In immunocompetent patients, severe CAP is severe because of the underlying cardiopulmonary status of the patient. Although some pathogens are inherently more virulent than others, e.g., Legionella is more virulent thanMoraxella catarrhalis, clinical severity is primarily determined by host rather than microbial factors. A patient with good cardiopulmonary function may present with severe CAP with Legionnaires’ disease, and a patient with severe chronic obstructive pulmonary disease (COPD) withM. catarrhalis CAP will present as a severe pneumonia. Patients with asplenia, although not strictly normal hosts, are usually considered as a variant of normal host. Patients with various degrees of hyposplenism if they have pneumonia, usually present as severe CAP. In contrast, compromised hosts in the usual sense refer to patients with congenital or acquired severe immune defects, e.g., human immunodeficiency virus (HIV) (1-3).
