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For further information, see CMDT Part 35-15: Legionnaires Disease

KEY FEATURES

  • An important cause of community-acquired pneumonia

  • Classically, Legionnaires disease is caused by Legionella pneumophila, though other Legionella species can cause identical disease

  • Occurs more commonly in immunocompromised persons, in smokers, and in those with chronic lung disease

  • Outbreaks have been associated with contaminated water sources, such as shower heads and faucets in patient rooms and air conditioning cooling towers

CLINICAL FINDINGS

  • Many features of typical pneumonia, with high fevers, a toxic appearance, pleurisy, and grossly purulent sputum

  • Nausea, vomiting and diarrhea may be prominent

  • There may be relative bradycardia

DIAGNOSIS

  • There may be hyponatremia, hypophosphatemia, elevated liver enzymes, and elevated creatine kinase

  • Testing sputum samples using polymerase chain reaction is a highly sensitive method for diagnosing Legionella

  • Culture of Legionella species has up to 80% sensitivity

  • Culture onto charcoal-yeast extract agar or similar enriched medium

    • Most sensitive method for diagnosis

    • Permits identification of infections caused by species and serotypes other than L pneumophila serotype 1

  • Dieterle silver staining of tissue, pleural fluid, or other infected material is also a reliable method for detecting Legionella species

  • Direct fluorescent antibody sputum stains may also be performed

  • Legionella serology and urinary antigen are less sensitive diagnostic methods; the latter will detect only L pneumophila serotype 1

TREATMENT

  • Medications of choice

    • Azithromycin, 500 mg orally or intravenously once daily, or

    • A fluoroquinolone (eg, levofloxacin, 750 mg orally or intravenously once daily)

  • Duration of therapy is generally 7–10 days, although a 14- to 21-day course of therapy is recommended for immunocompromised patients or those with severe disease

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