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  • • Typical symptoms include dyspnea, cough with or without sputum production, fever or hypothermia, chest pain, and chills.
  • • Presence of a parenchymal infiltrate on chest radiograph distinguishes pneumonia from acute bronchitis.
  • • Hospital-acquired pneumonia occurs more than 48 h after admission to the hospital and excludes any infection that is present at the time of admission.
  • • Hospital-acquired pneumonia is especially common in patients who require mechanical ventilation.

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Bacterial pneumonia has been recognized as a common infection for nearly two centuries and remains the sixth leading cause of death in the United States. Community-acquired pneumonia (CAP) is defined as an infection that begins outside of the hospital or is diagnosed within 48 h after admission to the hospital in a patient who has not resided in a long-term facility for 14 days or more before the onset of symptoms. CAP is a major health concern in the United States, accounting for 3.3 to 4 million cases per year. The annual economic impact of CAP includes $20 billion in patient care expenses and lost wages, 64 million days of restricted activity, 39 million days of bed confinement, and 10 million days of work loss. Up to 20% of patients with CAP require hospitalization, resulting in 600,000 to 1,000,000 hospital admissions per year.

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Hospital-acquired pneumonia (HAP) is defined as infection of lung parenchyma occurring more than 48 h after admission to a hospital. When HAP occurs in the subset of patients receiving mechanical ventilation it is termed ventilator-associated pneumonia (VAP). HAP is a common nosocomial infection with a rate of between 5 and 10 cases per 1000 hospital admissions. The incidence in patients who require mechanical ventilation is 6 to 20 times higher. HAP is the leading cause of death from hospital-acquired infections.

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Bacteria are deposited in terminal bronchioles and alveolar spaces by several mechanisms. These include aspiration of oropharyngeal or gastric contents, inhalation of bacterial laden aerosols, and hematogenous translocation from an infected site to the lung. Aspiration and inhalational mechanisms of entry account for the majority of pulmonary infections. The severity of pneumonia depends on the amount of material aspirated, the quantity of bacteria in the aspirate, the virulence of the organism, and the integrity of host defenses. Community-acquired pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus colonize normal hosts. Colonization by gram- negative bacilli is less common but these organisms are important pathogens in patients with alcoholism, diabetes mellitis, and poor oral hygiene and in the institutionalized elderly. Inhalational entry of organisms is associated with specific pathogens that are able to reach the lower airway. These highly efficient pathogens include Legionella species, Mycoplasma pneumoniae, Chlamydia species, and Coxiella burnetii; they share the ability to resist phagocytosis or to survive intracellularly within phagocytes.

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Depending on the virulence of the pathogen and the strength of the patient’s host defense system, an intense inflammatory process ensues after propagation of organisms in the ...

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