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Key Points

  • Focus on diagnosing pneumonia early.

  • Identify risk factors that influence treatment decisions (eg, antibiotic choice and disposition).

  • Blood cultures and empiric antibiotics should be started in the emergency department for patients admitted with pneumonia.

  • Tuberculosis should be considered for patients with human immunodeficiency virus or other significant risk factors to avoid further spread.


Pneumonia is the sixth leading cause of death and the leading cause of death from an infectious disease in the United States. The annual incidence of community-acquired pneumonia (CAP) in the United States is 4 million cases, and it results in about 1 million hospitalizations. Most deaths occur in the elderly or immunocompromised.

Pneumonia is an infection of the pulmonary alveoli caused by aspiration, inhalation, or hematogenous seeding of pathogens. An inflammatory response in the alveoli leads to sputum production and a cough, although atypical organisms may produce other findings such as mental status changes or weakness.

Pneumonia can be divided into 4 categories based on where it is acquired. CAP occurs in patients who have not been recently in a nursing home or hospitalized. Hospital-acquired pneumonia (HAP) occurs more than 2 days after hospital admission. Ventilator-associated pneumonia (VAP) occurs 2–3 days after endotracheal intubation. Health care–associated pneumonia (HCAP) occurs within 90 days of a 2-day hospital stay; in a nursing home resident; within 30 days of receiving IV antibiotics, chemotherapy, or wound care, or after a hospital or hemodialysis clinic visit; or in any patient in contact with a multidrug-resistant pathogen.

In about half of cases of pneumonia, the etiology will not be determined. In those whose cause can be determined, “typical” pathogens (Streptococcus pneumoniae, Haemophilus influenzae, and Klebsiella pneumoniae) account for about 25%, with S. pneumoniae being the most common bacterial pathogen identified. “Atypical” pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella) account for 15%. Viral pathogens (influenza, parainfluenza, and adenovirus) account for about 17%. HCAP may also be due to other agents, including Pseudomonas aeruginosa, Staphylococcus aureus, and Enterobacter species. In patients with diminished mental status, aspiration of a foreign substance (eg, gastric contents) into the lungs leads to a pneumonitis and a polymicrobial infection. Determining risk factors, such as comorbidities, alcohol abuse, and the patient's environment, can help guide therapies and disposition decisions.

Clinical Presentation


In most adults and adolescents, the diagnosis of pneumonia can be made by history and physical examination alone. Patients will typically complain of a cough productive of purulent sputum, fevers, shortness of breath, fatigue, and pleuritic chest pain. Patients at the extremes of age (children and the elderly) and immunocompromised patients often present with atypical symptoms. In many cases, they present with mental status changes or deterioration of baseline function alone.

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