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Key Features

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Essentials of Diagnosis
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  • Severe progressive pneumonia in a child with compromised immunity

  • Diarrhea and neurologic signs are common

  • Direct fluorescent antibody staining of respiratory secretions and urinary antigen tests are highly specific but do not identify all infections

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General Considerations
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  • Legionella pneumophila causes two distinct clinical syndromes: Legionnaires disease and Pontiac fever

  • Contaminated cooling towers and heat exchangers have been implicated in several large institutional outbreaks

  • Person-to-person transmission has not been documented

  • Few cases of Legionnaires disease have been reported in children;most were in children with compromised cellular immunity

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Clinical Findings

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Symptoms and Signs
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  • Legionnaires disease

    • Abrupt onset of fever, chills, anorexia, and headache

    • Pulmonary symptoms appear within 2–3 days and progress rapidly

    • Cough is nonproductive early

    • Purulent sputum occurs late

    • Hemoptysis, diarrhea, and neurologic signs (including lethargy, irritability, tremors, and delirium) are seen

  • Pontiac fever is a milder, self-limited illness without evidence of pneumonia

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Differential Diagnosis
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  • Other bacterial pneumonias

  • Viral pneumonias

  • Mycoplasma pneumonia

  • Fungal disease

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Diagnosis

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Laboratory Findings
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  • WBC count is usually elevated in Legionnaires disease

  • Cultures from sputum, tracheal aspirates, or bronchoscopic specimens, when grown on specialized media are positive in 70–80% of patients at 3–5 days of culture

  • Direct fluorescent antibody staining of sputum or other respiratory specimens is only 50–70% sensitive but 95% specific

  • PCR detection of respiratory secretions for Legionella is available at some centers

  • Urine antigen tests for Legionella antigen are highly specific, but only detect L pneumophila serotype 1, which is the most common community-acquired L pneumophila infection

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Imaging
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  • Chest radiographs

    • Show rapidly progressive patchy consolidation

    • Cavitation and large pleural effusions are uncommon

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Treatment

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  • Intravenous azithromycin, 10 mg/kg/d given as a once-daily dose (maximum dose 500 mg), is the drug of choice in most children

  • In immunocompromised patients, levofloxacin is recommended (not approved for this indication in children < 18 years of age) because fluoroquinolones are bactericidal agents.

  • Doxycycline (not recommended for children < 8 years of age unless benefit exceeds risk) and TMP-SMX are alternative agents

  • Duration of therapy is 5–10 days if azithromycin is used; for other antibiotics a 14- to 21-day course

  • Oral therapy may be substituted for intravenous therapy as the patient's condition improves

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Outcome

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Complications
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  • Hematogenous dissemination may result in extrapulmonary foci of infection, including pericardium, myocardium, and kidneys

  • Legionella may be the cause of culture-negative endocarditis

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Prevention
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  • No vaccine is available

  • Legionella is naturally found in water, so ensuring proper disinfectant and water temperature maintenance of water supplies helps prevent cases

  • Good cleaning, attention to pH, and proper disinfectants in hot tubs is important

  • Chlorine or monochloramine treatment of municipal water supplies has been shown to reduce the number of organisms and the risk of infection

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Prognosis
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