• Legionella Commonly Infects Immunocompetent Persons: presents as a severe community-acquired pneumonia

Risk Factors

  • Anti-Tumor Necrosis Factor-α (Anti-TNFα) Therapy (see Anti-Tumor Necrosis Factor-α Therapy, [[Anti-Tumor Necrosis Factor-α Therapy]]) (Clin Infect Dis, 2006) [MEDLINE]
    • Case Series of 10 Patients Reported from France
    • Agents
      • Adalimumab (xxx) (see Adalimumab, [[Adalimumab]])
      • Etanercept (xxx) (see Etanercept, [[Etanercept]])
      • Infliximab (xxx) (see Infliximab, [[Infliximab]])
    • Relative Risk: Adalimumab > Etanercept/Infliximab
  • Exposure in Large Hotel/Cruise Ship: symptoms usually occur weeks later
  • Exposure to Water Source
    • Condensers
    • Grocery Store Misters
    • Respiratory Care Devices
    • Showers
    • Whirlpools
  • Corticoteroid/Cytotoxic Administration: increases risk of nosocomial Legionella pneumonia (steroids also increase risk for community-acquired Legionella)
    • Previous antibiotic use and decreased consciousness were associated with a lower risk of nosocomial pneumonia


  • Legionella Species
    • Legionella Pneumophila
    • Legionella Maceachernii
    • Legionella Micdadei
  • Incubation: 2-10 days


Complete Blood Count (CBC) (see Complete Blood Count, [[Complete Blood Count]])

Sputum Gram Stain and Culture

  • May Show Numerous Neutrophils, But Few or No Organisms

Urinary Legionella Antigen (RIA or ELISA)

  • Technique
    • Easy Sample to Obtain
    • Rapid Turnaround Time: available within hours
  • Sensitivity/Specificity
    • 90-95% Sensitive for Culture-Proven Cases of Serogroup-1 Legionella Pneumophila
      • Does Not Detect Some Legionella Pneumophila Serogroups and Some Other Legionella Species: therefore, it should not be the only test used
    • Highly Specific
  • Duration of Urinary Antigen Excretion: antigen excretion can persist after illness is cured

Bronchoalveolar Lavage (BAL) Legionella Culture (see Bronchoscopy, [[Bronchoscopy]])

  • Culture is the Single Most Important Test for Legionella
  • Technique
    • Culture on Buffered Charcoal Yeast Extract (BCYE) Agar
      • Requires 3 days for Growth
      • Negative Results are Not Reported for 1 Week
  • Sensitivity/Specificity
    • Detects All Legionella Species and Subgroups
    • False-Positive Results are Rare

Bronchoalveolar Lavage (BAL) Legionella DFA (see Bronchoscopy, [[Bronchoscopy]])

  • Technique
    • Requires Lower Respiratory Tract Specimen
    • Results are Available Quickly
  • Sensitivity/Specificity
    • Monoclonal Reagents are Specific and Detect All Legionella Pneumophila Serogroups (But Not Other Legionella Species)
    • Specificity of Polyclonal Reagents Used for Serogroups Other than Legionella Pneumophila is Not Well-Defined

Legionella Serology

  • Useful for Epidemiologic and Research Purposes Only: too slow to be useful for clinical purposes

Clinical Manifestations of Pontiac Fever (see Pontiac Fever, [[Pontiac Fever]])

  • Exposure: inhalation of aerosols from Legionella-infected water source
  • Epidemiology: 36 hrs (much shorter than that for Legionnaires’ disease)
  • Diagnosis
  • Clinical
    • Cough (see Cough, [[Cough]])
    • Dyspnea (see Dyspnea, [[Dyspnea]])
    • Fever (see Fever, [[Fever]])
  • Treatment: self-limited febrile syndrome

Clinical Manifestations of Legionnaires’ Disease

General Comments

  • Time Course of Legionnaires’ Disease: while fever may precede the appearance of pulmonary infiltrates in some cases, almost all patients have infiltrates by day 3 of the illness


Chest Pain (see Chest Pain, [[Chest Pain]])

  • Epidemiology: occurs in 13-35% of cases

Myocarditis/Pericarditis/Prosthetic Valve Endocarditis (see Myocarditis, [[Myocarditis]], Acute Pericarditis, [[Acute Pericarditis]], and Endocarditis, [[Endocarditis]])

  • Epidemiology: extrapulmonary disease in Legionnaires’ Disease is extremely rare
    • Reported Mainly in Immunocompromised Patients

Gastrointestinal Manifestations

Abdominal Pain (see Abdominal Pain, [[Abdominal Pain]])

  • Epidemiology

Diarrhea (see Diarrhea, [[Diarrhea]])

  • Epidemiology: occurs in 21-50% of cases

Elevated Liver Function Tests (LFT’s)

  • Epidemiology: common

Nausea/Vomiting (see Nausea and Vomiting, [[Nausea and Vomiting]])

  • Epidemiology: occurs in 8-49% of cases

Neurologic Manifestations

Headache (see Headache, [[Headache]])

  • Epidemiology: occurs in 40-48% of cases

Neurologic Abnormalities

  • Epidemiology: occur in 4-53% of cases
  • Clinical

Pulmonary Manifestations

Acute Respiratory Distress Syndrome (ARDS) (see Acute Respiratory Distress Syndrome, [[Acute Respiratory Distress Syndrome]])

  • Epidemiology

Alveolar or Interstitial Pneumonia

  • Radiographic Patterns
    • Patchy Lobar Infiltrate, Which Progresses to Consolidation (see Pneumonia, [[Pneumonia]]): most common pattern
      • Cavitation is Uncommon: although may be seen in some immunocompromised cases though
    • Diffuse Interstitial Infiltrates (see Interstitial Lung Disease, [[Interstitial Lung Disease]]): has been reported (Chest, 2000) [MEDLINE]
    • Other Patterns: have been reported
  • Cough (see Cough, [[Cough]])
  • Dyspnea (see Dyspnea, [[Dyspnea]])
  • Rales
  • Streaky Hemoptysis (see Hemoptysis, [[Hemoptysis]]): gross hemoptysis is rare
  • Absence of Upper Respiratory Symptoms

Lymphocytic Interstitial Pneumonia (see Lymphocytic Interstitial Pneumonia, [[Lymphocytic Interstitial Pneumonia]])

  • Epidemiology

Pleural Effusion (see Pleural Effusion-Exudate, [[Pleural Effusion-Exudate]])

  • Epidemiology: small pleural effusion is noted in 20-50% of cases

Rounded Atelectasis (see Rounded Atelectasis, [[Rounded Atelectasis]])

  • Epidemiology: may occur in absence of significant pleural disease

Renal Manifestations

Acute Interstitial Nephritis (see Acute Interstitial Nephritis, [[Acute Interstitial Nephritis]])

  • Epidemiology

Hematuria (see Hematuria, [[Hematuria]])

  • Epidemiology: common

Hyponatremia (see Hyponatremia, [[Hyponatremia]])

  • Epidemiology: occurs more commonly in Legionellosis than in other pneumonias

Proteinuria (see Proteinuria, [[Proteinuria]])

  • Epidemiology

Rheumatologic Manifestations

Arthralgias/Myalgias (see xxxx, [[xxxx]])

  • Epidemiology: occur in 20-40% of cases

Other Manifestations

Fever (see xxxx, [[xxxx]])

  • Epidemiology
    • Fever >38.8ºC: occurs in 88-90% of cases
    • Fever >40ºC: occurs in 20-62% of cases




  • The radiologic manifestations of Legionnaire’s disease. The Ohio Community-Based Pneumonia Incidence Study Group. Chest. 2000;117(2):398 [MEDLINE]
  • Emergence of Legionella pneumophila pneumonia in patients receiving tumor necrosis factor-alpha antagonists. Clin Infect Dis 2006; 43:e95-e100 [MEDLINE]