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Productive cough and fever are usually the presenting symptoms in patients with pneumonia. Symptoms may worsen over days or develop abruptly. Pleuritic chest pain, shortness of breath, chills, and rigors may also occur.


  1. CAP typically refers to patients with signs, symptoms, and radiographic evidence of pneumonia without known immunocompromise, and that was not hospital acquired (developing more than 48 hours after admission).

  2. Most common cause of infectious death and hospitalization in the United States

  3. Epidemiology

    1. Epidemiology varies with location, time period and diagnostic tool utilized. The local epidemiology and time period are important considerations (ie, influenza season).

    2. S pneumoniae is usually the most common pathogen. Other bacterial pathogens include M pneumoniae, S aureus, Legionella, and others

    3. Viral infection is common. A meta-analysis revealed a viral pathogen in 44.2% of patients (in studies that sampled lower respiratory tract with BAL and sputum). Common viruses include human rhinovirus, influenza A and B, human metapneumovirus, respiratory syncytial virus, parainfluenza virus, coronavirus, and others.

    4. Viral-bacterial coinfection is surprisingly common in patients with CAP.

      1. Concomitant viral and bacterial infections occurred in 19–39% of all patients, 44% of patients with S pneumoniae.

      2. In one study of severe CAP, 79% of patients with a positive viral PCR also had bacterial infection.

      3. Furthermore, the odds ratio of death was higher in patients with concomitant infection 2.1 (1.3–3.3)

        image A positive viral PCR does not exclude concomitant bacterial CAP.

  4. 3.4% of pneumonia are associated with underlying malignancy (postobstructive pneumonia)

  5. Complications

    1. Respiratory failure

    2. Sepsis

    3. Death

    4. Empyema (See Disease Highlights).

  6. Prognosis is good overall.

    1. 8% hospitalization rate

    2. 95% radiographic cure in 1 month

    3. Mortality 1.2%


  1. The diagnosis of CAP is classically made in patients with a combination of infectious symptoms (fever, chills, or rigors), respiratory symptoms (dyspnea) and signs (cough, chest pain, and crackles), and infiltrate on chest film.

  2. However, patients often lack 1 or more of these elements.

  3. As noted in Table 10-1 neither the absence of fever nor a normal lung exam individually rules out pneumonia (LR–, 0.6–0.8), so clinicians must maintain a high level of vigilance. However, the absence of both fever and abnormal lung findings makes the diagnosis unlikely (LR–, 0.08).

  4. Imaging

    1. Chest radiograph

      1. Most commonly used test to diagnose or exclude pneumonia but imperfect

      2. Sensitivity 71–78%, specificity 59–91% when compared with chest CT scan or discharge diagnosis (LR+, 1.9–8.1; LR–, 0.3–0.4). Additionally, a single anterior-posterior chest film has a lower sensitivity than posteroanterior and lateral views (59% vs 90%).

        image Posteroanterior and lateral chest film views are superior to single anterior-posterior views and should be obtained when possible.

      3. False-negative chest films were more common in patients with crackles on exam or a high C-reactive protein.

        image A normal chest radiograph does not rule out pneumonia when the pretest probability is high (ie, a patient with cough, fever, and crackles). Such patients should still receive antibiotics.

      4. Sensitivity may be ...

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