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Pneumonia is an infection of the alveolar or gas-exchanging portions of the lung. Community-acquired pneumonia (CAP) accounts for approximately 4 million cases and 1 million hospitalizations per year in the U.S.1,2 It is the sixth leading cause of death, particularly among older adults. The incidence of pneumonia caused by atypical or opportunistic infections is increasing. Recurring epidemics of severe acute respiratory syndrome or pandemic influenza may alter future recommendations for the evaluation and management of this disease. Pneumococcal pneumonia produces typical symptoms of fever, cough, and rigors, but atypical infections, infections in compromised hosts, and infections in patients at the extremes of age may produce atypical findings, such as a change in mental status or a decline in function. Patients with health care–associated pneumonia are at risk for infection with resistant organisms. The patient’s environment must be considered when predicting the causative organism and selecting treatment choices (Table 68-1).3,4 The most important environments to be considered in the ED are CAP and health care–associated pneumonia.

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Table 68-1 Acquisition Environment Classification for Pneumonia 
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Pathophysiology

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Pathogenic organisms may be inhaled or aspirated directly into the lungs. Some bacteria, such as Staphylococcus aureus or Pneumococcus, can produce pneumonia as a result of hematogenous seeding. Patients most at risk for pneumonia are those with a predisposition to aspiration, impaired mucociliary clearance, or risk of bacteremia (Table 68-2).

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Table 68-2 Risk Factors for Pneumonia 
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Some forms of pneumonia produce an intense inflammatory response within the alveoli that leads to filling of the air space with organisms, exudate, and white blood cells. Organisms can distribute throughout the lung by spreading along the bronchial tree or through pores between adjacent alveoli (pores of Kohn). Bacterial pneumonia results in an intense inflammatory response and tends to cause a productive cough. Atypical ...

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