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Pneumonia is a common cause of infection-related mortality and is one of the most important challenges in clinical medicine. Inappropriate or delayed treatment of pulmonary infection contributes to poor clinical outcomes, avoidable drug exposures, and emergence of antimicrobial resistance. Pneumonia is defined as inflammation of the pulmonary parenchyma caused by an infectious agent. The clinical syndrome of pneumonia may include fever or hypothermia, sweats, rigors, or chills, pulmonary symptoms, such as cough, sputum production, dyspnea, pleurisy, or pulmonary lesions observed on radiographic examination. Nonspecific symptoms are common, including loss of appetite, fatigue, and confusion. The diagnosis and management of pneumonia has been complicated by the recognition of newer pathogens, expanded antimicrobial resistance, increased populations of immunocompromised patients, and by newer diagnostic tools and antimicrobial agents.

Pneumonitis reflects inflammation due to both infection and noninfectious causes. A variety of eponyms have been applied to various forms of pneumonia that may reflect the epidemiology of the process and the likely causative organisms: aspiration pneumonia, community-acquired pneumonia (CAP), nosocomial pneumonia, immunocompromised host, and atypical pneumonia (Table 122-1). These descriptions, coupled with the radiologic appearance and patient-specific epidemiologic factors, are useful in considering empiric therapy while awaiting microbiologic data. These categories may be misleading, emphasizing the importance of obtaining a definitive microbiologic diagnosis in optimizing clinical care (Table 122-2).

Table 122-1Categorization of Pneumonia by Clinical Setting
Table 122-2Routine Evaluation of Patients with Suspected Pneumonia

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