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For further information, see CMDT Part 9-12: Pneumonia

KEY FEATURES

Essentials of Diagnosis

  • Fever or hypothermia, tachypnea, cough with or without sputum, dyspnea, chest discomfort, sweats or rigors (or both)

  • Bronchial breath sounds, rhonchi, or inspiratory crackles on chest auscultation

  • Parenchymal opacity on chest radiograph (occasionally not evident at presentation)

  • Occurs outside of the hospital or within 48 hours of hospital admission

General Considerations

  • The deadliest infectious disease in the United States and routinely among the top 10 causes of death

  • Risk factors for the development of community-acquired pneumonia (CAP) include

    • Older age

    • Excessive alcohol use

    • Tobacco use

    • Comorbid medical conditions, especially chronic obstructive pulmonary disease (COPD) or other chronic lung disease

    • Immunosuppression

    • Recent viral upper respiratory tract infection (URI)

  • Prospective studies fail to identify the cause in 30–60% of cases, although bacteria are more commonly identified than viruses

  • The most common bacterial pathogens

    • Streptococcus pneumoniae (two-thirds of cases)

    • Haemophilus influenzae

    • Mycoplasma pneumoniae

    • Chlamydophila pneumoniae

    • Staphylococcus aureus

    • Neisseria meningitidis

    • Moraxella catarrhalis

    • Klebsiella pneumoniae

  • Common viral causes

    • Coronaviruses (SARS-CoV-2, MERS)

    • Influenza

    • Respiratory syncytial virus

    • Adenovirus

    • Parainfluenza virus

  • Assessment of epidemiologic risk factors helps in diagnosing pneumonia due to

    • Chlamydophila psittaci (psittacosis)

    • Coxiella burnetii (Q fever)

    • Francisella tularensis (tularemia)

    • Endemic fungi (Blastomyces, Coccidioides, Histoplasma)

    • Sin Nombre virus (hantavirus pulmonary syndrome)

CLINICAL FINDINGS

Symptoms and Signs

  • Acute or subacute onset of fever, cough with or without sputum, and dyspnea

  • Rigors, sweats, chills, pleurisy, chest discomfort, and hemoptysis are common

  • Fatigue, anorexia, headache, myalgias, and abdominal pain can be present

  • Persons > age 80 may have an atypical presentation, including falls, delirium, lethargy, and anorexia

  • Physical findings include

    • Fever or hypothermia

    • Tachypnea

    • Tachycardia

    • Arterial oxygen desaturation

  • Chest examination often reveals inspiratory crackles, rhonchi, and bronchial breath sounds

  • Dullness to percussion may be found if lobar consolidation or a parapneumonic effusion is present

Differential Diagnosis

  • Bacterial pneumonia

  • Viral pneumonia

  • Aspiration pneumonia

  • Pneumocystis jirovecii pneumonia

  • Bronchitis

  • Lung abscess

  • Tuberculosis

  • Pulmonary embolism

  • Myocardial infarction

  • Sarcoidosis

  • Lung neoplasm

  • Hypersensitivity pneumonitis

  • Bronchiolitis

DIAGNOSIS

Laboratory Tests

  • See Table 9–9

  • Sputum Gram stain and culture

    • Test characteristics vary by organism and lack sensitivity for some of the most common causes of CAP

    • Usefulness lies in broadening initial coverage, most commonly to cover

      • S aureus (including community-acquired methicillin-resistant strains)

      • Gram-negative rods (including P aeruginosa and Enterobacteriaceae)

  • Urinary antigen assays for Legionella pneumophila and S pneumoniae

    • At least as sensitive and specific as sputum Gram stain and culture

    • Results are not affected by initiation of antibiotic therapy

    • Positive tests may allow narrowing of initial antibiotic coverage

    • Indications for urinary antigen assay for L pneumophila

      • Active alcohol use

      • Travel within 2 weeks

      • Pleural effusion

      • Intensive care unit (ICU) admission

    • Indications for urinary antigen assay for ...

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