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COMMUNITY-ACQUIRED PNEUMONIA

INTRODUCTION AND EPIDEMIOLOGY

Pneumonia is an infection of the alveolar (gas-exchanging) portion of the lung. Community-acquired pneumonia (CAP) accounts for approximately 3 million cases and 1.6 million hospitalizations per year in the United States.1,2 One third of pneumonia cases occur in adults over age 65 years, and approximately 4 in 100 children will develop pneumonia each year. According to 2016 data, 544,000 ED visits were due to pneumonia. Pneumonia accounts for 16.1 deaths per 100,000 population, making it the eighth leading cause of death, particularly among older adults, with an age-adjusted death rate of 22%.

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 healthcare–associated pneumonia are at risk for infection with resistant organisms. When predicting the causative organism and selecting treatment choices in pneumonia patients, think of the acquiring environment, especially community versus healthcare settings (Table 65-1).3,4

TABLE 65-1Acquisition Environment Classification for Pneumonia

PATHOPHYSIOLOGY

Pathogenic organisms are inhaled or aspirated directly into the lungs, with aspiration being more common, especially in healthcare settings. Some bacteria, such as Staphylococcus aureus or Pneumococcus, may produce pneumonia by hematogenous seeding. Patients most at risk for pneumonia are those with a predisposition to aspiration, with impaired mucociliary clearance, or likely to have bacteremia (Table 65-2).

TABLE 65-2Risk Factors for Pneumonia

Some forms of pneumonia produce an intense inflammatory response within the alveoli that leads to filling of the air space with exudate and WBCs. Organisms can distribute throughout the lung by spreading along the bronchial tree ...

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