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Epidemiology, pathogenesis, and microbiology of community-acquired pneumonia in adults

Thomas J Marrie, MD
Thomas M File, Jr, MD
Section Editor
John G Bartlett, MD
Deputy Editor
Anna R Thorner, MD


Community-acquired pneumonia (CAP) is defined as an acute infection of the pulmonary parenchyma in a patient who has acquired the infection in the community, as distinguished from hospital-acquired (nosocomial) pneumonia (HAP). A third category of pneumonia, designated healthcare-associated pneumonia (HCAP), is acquired in other healthcare facilities such as nursing homes, hemodialysis centers, and outpatient clinics. The rationale for the separate designation of HCAP was that patients with HCAP were at higher risk for multidrug-resistant (MDR) organisms. However, several studies have shown that many patients defined as having HCAP are not at high risk for MDR pathogens [1-3]. Furthermore, although interaction with the healthcare system is potentially a risk for MDR pathogens, underlying patient characteristics are also important independent determinants of risk for MDR pathogens.

CAP is a common and potentially serious illness [4-6]. It is associated with considerable morbidity and mortality, particularly in older adult patients and those with significant comorbidities. (See "Prognosis of community-acquired pneumonia in adults".)

The epidemiology, pathogenesis, and microbiology of CAP in adults will be reviewed here. A variety of other important issues related to CAP are discussed separately. These include:

The diagnostic approach to patients with CAP (see "Diagnostic approach to community-acquired pneumonia in adults")

The use of sputum cultures for the evaluation of bacterial pneumonia (see "Sputum cultures for the evaluation of bacterial pneumonia")


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Literature review current through: Sep 2016. | This topic last updated: May 5, 2016.
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