Legionella Infection

Key Features

Essentials of Diagnosis

• 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

General Considerations

• 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

Clinical Findings

Symptoms and Signs

• 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

Differential Diagnosis

• Other bacterial pneumonias

• Viral pneumonias

• Mycoplasma pneumonia

• Fungal disease

Diagnosis

Laboratory Findings

• 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

Imaging

• Chest radiographs

  • Show rapidly progressive patchy consolidation

  • Cavitation and large pleural effusions are uncommon

Treatment

• 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

Outcome

Complications

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

• Legionella may be the cause of culture-negative endocarditis

Prevention

• 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 ...