• See Also
  1. Bacterial Pneumonia
  2. Waterborne Illness
  • Epidemiology
  1. Legionella pneumophila accounts for 2% (up to 10% in some case series) of hospitalized Pneumonia cases
  2. Legionella Outbreaks in U.S.
    1. American Legion Convention in Philadelphia (1976)
      1. Legionnaire's Disease is named for this outbreak with 182 Legionella pneumonia cases, and 29 deaths
      2. Legionella was ultimately found colonizing the cooling tower of the hotel's air conditioning system
    2. Health department in Pontiac, Michigan (1967)
      1. Pontiac Fever (milder Legionella infection without Pneumonia) is named for this outbreak
      2. Outbreak affected 144 (nearly 95% of exposed health department staff members, but no deaths)
  • Pathophysiology
  1. Legionella pneumophila
    1. Aerobic Gram Negative Rod
    2. Virulent organism that infects the respiratory tract
    3. Facultative Intracellular Parasite
      1. Legionella multiplies within Alveolar Macrophages
      2. When phagocytosed by Macrophages, Legionella survives
        1. Inhibits Lysosome-Phagosome fusion
        2. Deactivates superoxide and Hydrogen Peroxide radicals
    4. Virulence factors
      1. Dot/Icm Type IV Secretion System (T4SS)
        1. Inhibits Lysosome-Phagosome fusion within Macrophages (allowing Legionella to survive)
      2. Copper-zinc superoxide dismutase (CuZnSOD) and Catalase-peroxidase
        1. Protects Legionella against oxidation by Macrophage superoxide and Hydrogen Peroxide
      3. Attachment and Invasion Factors
        1. Bacterial Pilli
        2. Flagella
      4. Protein Toxins
        1. Phospholipase A
        2. Phospholipase C
        3. RNAase
  2. Transmission
    1. Inhalation of aerosolized contaminated water
      1. No person to person transmission
    2. Optimal conditions for growth
      1. Temperature: 89 to 113 F water
      2. Stagnant water
      3. Legionella survives for long periods at low metabolic states in a biofilm
        1. Released in large numbers when the biofilm is disturbed
    3. Waterborne Illness
      1. Freshwater or moist soil near ponds
      2. Air conditioning
      3. Condensers
      4. Cooling towers
      5. Respiratory therapy equipment
      6. Showers, shower heads or water faucets
      7. Whirlpools
      8. Aeorsolized mist (hot tubs, decorative fountains, market produce mist machines)
      9. Potting Soil
  3. Incubation
    1. Two to ten days
  • Risk Factors
  1. Tobacco Smoking
  2. Chronic Renal Failure
  3. Malignancy
  4. Immunosuppression
  5. Diabetes Mellitus
  6. Chronic Liver Disease
  7. Exposure to recent plumbing work
  8. Overnight stay outside the home
  • Types
  • Presentations
  1. Legionellosis or Legionnaire's Disease
    1. Severe illness including Legionella pneumonia
    2. Legionella pneumonia is a more severe disease than other Atypical Pneumonias
    3. This page primarily refers to Legionnaire's Disease (rather than the more mild Pontiac Fever)
  2. Pontiac Fever
    1. Mild, Influenza-like illness without associated Pneumonia (unlike Legionnaire's Disease)
    2. Prodrome of Headaches, myalgias and Fatigue followed by fever and chills
    3. Resolves within 5-7 days
  • Findings
  • Legionnaire's Disease
  1. Prodrome for 12-48 hours
    1. Malaise
    2. Myalgia
    3. Headache
  2. Next symptoms for 2-3 days
    1. Fever to 40.5 C
      1. Persists for 8-10 days
      2. Pulse-Temperature Dissociation (Relative Bradycardia for high fever)
    2. Gastrointestinal symptoms in 20-40% of cases
      1. Nausea or Vomiting
      2. Diarrhea
      3. Abdominal Pain
  3. Later Symptoms
    1. Cough
      1. Purulent Sputum production in only 50% of cases (when present may be minimal)
      2. Slightly blood tinged Sputum
    2. Severe respiratory distress
    3. Confusion
    4. Disorientation
  • Complications
  1. Respiratory Failure (20-40% of Legionnaires cases)
  2. Extrapulmonary complications
    1. Myocarditis or Pericarditis
    2. Prosthetic Valve Endocarditis
    3. Glomerulonephritis
    4. Pancreatitis
    5. Peritonitis
    6. Rhabdomyolysis
  1. Small Pleural Effusions
  2. Unilateral parenchymal infiltrates
    1. Round, fluffy opacities
    2. Spread contiguously to other lobes
    3. Progresses to dense consolidation
    4. Progresses to bilateral infiltrates
  • Labs
  1. Complete Blood Count
    1. Leukocytosis
    2. Leukopenia
  2. Acute Phase Reactants (C-Reactive Protein, Erythrocyte Sedimentation Rate)
    1. Elevated markedly
  3. Comprehensive Metabolic panel and other Electrolytes
    1. Hyponatremia
    2. Hypophosphatemia
    3. Elevated hepatic enzymes
  4. Creatine Phosphokinase (CPK)
    1. May be elevated associated with Rhabdomyolysis
  5. Sputum Exam
    1. Fluorescent Antibody studies of Sputum
    2. Legionella can not be seen on Gram Stain
  • Diagnosis
  1. Legionella urine Antigen testing
    1. High sensitivity and Specificity for serogroup 1
      1. Serogroup 1 (LP1) causes most U.S. cases (80-90%)
    2. Sputum Culture required to identify other serogroups
      1. Urine Antigen and Sputum Culture all cases
    3. References
      1. Benin (2002) Clin Infect Dis 35:1039-46 [PubMed]
  2. Concurrent Sputum and Blood Culture in all suspected cases (before Antibiotics)
    1. Sputum Culture on special medium
  3. Legionella Serologies
    1. Legionella fourfold titer rise to >= 1:128 or
    2. Legionella titer >= 1:256
  • Management
  1. Antibiotic course
    1. Immunocompetent: 7-10 days
    2. Immunocompromised: 14 to 21 days
  2. Legionella pneumonia
    1. First-Line
      1. Azithromycin 500 mg IV or Oral every 24 hours
      2. Levofloxacin 750 mg IV or Oral every 24 hours
      3. Moxifloxacin 400 mg IV or Oral every 24 hours
    2. Alternatives
      1. Doxycycline 100 mg IV or Oral every 12 hours
      2. Clarithromycin 500 mg IV or Oral every 12 hours
      3. Erythromycin 500 to 1000 mg IV or Oral every 6 hours
  3. Legionella Endocarditis
    1. Antibiotic selection based on cultures and infectious disease Consultation
    2. Doxycycline 200 mg IV or oral every 12 hours
    3. Ciprofloxacin 400 mg IV every 12 hours or 500 mg orally twice daily
    4. Erythromycin 500 mg IV or Oral every 6 hours AND Rifampin 600 to 1200 mg divided twice daily orally
  • Course
  1. Response to Antibiotics may not be seen for 4-5 days
  2. Up to 10-15% mortality in some studies
  • References
  1. (2023) Sanford Guide, accessed 2/6/2025
  2. Akbas (2001) Postgrad Med 109(5):135-47 [PubMed]
  3. File (1998) Infect Dis Clin North Am 12(3):569-92 [PubMed]
  4. Klein (1998) Semin Respir Infect 13(2):140-6 [PubMed]
  5. Iliadi (2022) J Clin Med 11(20):6126 +PMID: 36294446 [PubMed]
  6. Perkins (2017) Am Fam Physician 95(9):554-60 [PubMed]
  7. Plouffe (2000) Clin Infect Dis 31:S35-9 [PubMed]
  8. Tan (1999) Can Respir J 6:15A-9A [PubMed]
  9. Waterer (2001) Am J Med 110(1):41-8 [PubMed]