Fact-sheet: Legionella pneumonia


Updated on 04/19/2018 at 6:48 PM

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Definition

Legionella pneumophila infection responsible for acute community-acquired pneumonia in immunocompetent patients, or severe pneumonia in immunocompromised patients.

  • Incidence rate in France: 1.9/100,000 inhabitants
  • 5% of community-acquired pneumonias
  • Case fatality rate of 14% in France
  • Causative agent: Legionella pneumophila (Gram-negative bacillus), serogroup 1 in 90% of cases.
  • Transmission occurs via the respiratory route, through inhalation of contaminated water aerosols. No documented human-to-human transmission.
  • Notifiable disease
  • Known since the 1976 outbreak among American Legion veterans gathered at a convention in Philadelphia.

Clinical features

Severe-appearing pulmonary infection, acute onset, bilateral involvement

No ENT signs,

Relative bradycardia,

Presence of extrathoracic signs:

  • digestive (abdominal pain, vomiting, diarrhea);
  • neurologic (altered consciousness, headache, no meningeal syndrome).

Laboratory findings

Positive diagnosis by urinary antigen testing, but only for serogroup Lp1.

This test becomes positive 24-48h after exposure and remains detectable for up to 2 months afterward.

Suggestive laboratory findings:

  • hepatic cytolysis,
  • glomerular syndrome and/or renal failure,
  • hyponatremia,
  • hypophosphatemia,
  • elevated CPK.

Radiography

Lobar pneumonia: multilobar airspace pattern

Air bronchogram within the consolidations

CT

Lobar pneumonia: multiple airspace consolidations, multilobar involvement

Air bronchogram within the consolidations

Airspace filling predominating peripherally

In immunocompromised patients:

  • nodular forms
  • progression to abscess formation
  • progression to parenchymal necrosis
  • Pneumatocele

Management

Antibiotic therapy:

  • in common forms: monotherapy, either a macrolide or a quinolone
  • in severe forms or in an immunocompromised host, dual IV antibiotic therapy

Treatment duration is classically 14 to 21 days in immunocompetent patients.

It may be extended to 30 days in immunocompromised patients or in severe forms.