Legionella

Aka: Legionella, Legionella pneumophila, Legionella pneumonia, Legionnaire's Disease, Legionellosis, Pontiac Fever

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II. 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)

III. 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

IV. 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

V. 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

VI. 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

VII. 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

VIII. Imaging: Chest XRay

  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

IX. 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

X. 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

XI. 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

XII. Course

  1. Response to Antibiotics may not be seen for 4-5 days
  2. Up to 10-15% mortality in some studies

XIII. 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]

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Related Studies

Ontology: Legionellosis (C0023240)

Definition (MSH) Infections with bacteria of the genus LEGIONELLA.
Definition (CSP) gram negative bacterial infection by any species of Legionella including Legionnaire's disease, which is characterized by high fever, malaise, muscle aches, respiratory disorders and headache.
Concepts Disease or Syndrome (T047)
MSH D007876
SnomedCT 26726000
LNC LA10483-8
English Legionelloses, Legionella infections, Legionellosis [Disease/Finding], legionella infection, legionellosis, Legionella infection NOS, Legionella infection, Legionella infection (disorder), Legionella infection, NOS, Legionellosis, NOS, Legionellosis
Italian Infezione da legionella, Infezioni da legionella, Infezione da Legionella NAS, Legionellosi
Dutch Legionella-infectie NAO, Legionella-infecties, Legionella-infectie, Legionellose
French Infection à Légionella SAI, Infections à Legionella, Infection à Légionella, Légionellose, Infection à Legionella, Infection à légionelles
German Legionella NNB, Legionella-Infektionen, Legionelleninfektion, Legionellose
Portuguese Infecção por legionela NE, Infecção por legionela, Infecções a legionela, Legionelose
Spanish Legionella NEOM, infección por Legionella, legionelosis (trastorno), legionelosis, Legionella, Infecciones por legionella, Legionelosis
Japanese レジオネラ感染ＮＯＳ, レジオネラ感染, ﾚｼﾞｵﾈﾗｶﾝｾﾝNOS, ﾚｼﾞｵﾈﾗｶﾝｾﾝ
Swedish Legionella-infektioner
Czech legionelóza, Legionelová infekce, Legionelové infekce, Legionelová infekce NOS
Finnish Legionelloosi
Russian LEGIONELLEZ, ЛЕГИОНЕЛЛЕЗ
Croatian Not Translated[Legionellosis]
Polish Legioneloza, Legionelloza
Hungarian Legionella fertőzés k.m.n., Legionella fertőzés, Legionella fertőzések
Norwegian Legionellainfeksjoner, Legionellose
Derived from the NIH UMLS (Unified Medical Language System)

Ontology: Legionnaires' Disease (C0023241)

Definition (MEDLINEPLUS)

Legionnaires' disease is a type of pneumonia caused by bacteria. You usually get it by breathing in mist from water that contains the bacteria. The mist may come from hot tubs, showers, or air-conditioning units for large buildings. The bacteria don't spread from person to person.

Symptoms of Legionnaires' disease include high fever, chills, a cough, and sometimes muscle aches and headaches. Other types of pneumonia have similar symptoms. You will probably need a chest x-ray to diagnose the pneumonia. Lab tests can detect the specific bacteria that cause Legionnaires' disease.

Most people exposed to the bacteria do not become sick. You are more likely to get sick if you

  • Are older than 50
  • Smoke
  • Have a chronic lung disease
  • Have a weak immune system

Legionnaires' disease is serious and can be life-threatening. However, most people recover with antibiotic treatment.

Centers for Disease Control and Prevention
Definition (MSH) An acute, sometimes fatal, pneumonia-like bacterial infection characterized by high fever, malaise, muscle aches, respiratory disorders and headache. It is named for an outbreak at the 1976 Philadelphia convention of the American Legion.
Concepts Disease or Syndrome (T047)
MSH D007877
ICD9 482.84
ICD10 A48.1
SnomedCT 312403005, 154315008, 74881002, 266186009, 195889001, 269574000
English Disease, Legionnaire, Disease, Legionnaires', Infection, Legionella pneumophila, Infections, Legionella pneumophila, Legionella pneumophila Infection, Legionella pneumophila Infections, Legionnaire Disease, Legionnaires Disease, pneumophila Infection, Legionella, pneumophila Infections, Legionella, Legionnaire's Disease, Legionnaires' disease, LEGIONELLA PNEUMOPHILA INFECT, INFECT LEGIONELLA PNEUMOPHILA, LEGIONNAIRES DIS, LEGIONNAIRE DIS, Legionnaire's disease (diagnosis), Pneumonia legionella, Legionellal pneumonia, Legionnaire disease, Legionnaires' Disease [Disease/Finding], disease legionnaire's, legionella pneumonia, Disease;Legionnaires, disease legionnaires's, diseases legionnaire's, diseases legionnaires, legionnaire disease, pneumonia legionella, legionnaires disease, legionnaires' disease, Pneumonia due to Legionnaires' disease, Legionella, (Legionella) or (Legionnaire's disease) (disorder), (Legionella) or (Legionnaire's disease), Legionella pneumophila infection, Legionnaire's disease, Infection by Legionella pneumophilia, Legionella pneumonia, Infection by Legionella pneumophilia (disorder), Legionella pneumonia (disorder), Legionnaire's disease (disorder), Legionella pneumophila; infection, pneumonia (manifestation), Legionella pneumophila; infection, disease (or disorder); legionnaire's, infection; Legionella pneumophila, pneumonia (manifestation), infection; Legionella pneumophila, legionnaire's disease, legionnaire's; disease, Legionella pneumonia, NOS, Legionnaire's disease [Ambiguous], Legionnaires' Disease, Legionnaires disease
Italian Polmonite da Legionella, Infezione da legionella pneumophila, Malattia del legionario, Infezioni da Legionella pneumophila, Malattia dei legionari
Dutch legionairsziekte, Legionella pneumophila-infectie, Legionella pneumophila; infectie, pneumonie, Legionella pneumophila; infectie, aandoening; legionnair, infectie; Legionella pneumophila, pneumonie, infectie; Legionella pneumophila, legionnair; aandoening, Legionellose [veteranenziekte], Legionella-pneumonie, Legionairsziekte, Legionella-pneumophila-infectie, Veteranenziekte, Ziekte, legionairs-
French Pneumonie à Legionella, Infection à Legionella pneumophila, Pneumonie à Légionelles, Maladie des légionnaires, Infections à Legionella pneumophila, Maladie du légionnaire
German Legionella pneumophila Infektion, Legionaerskrankheit, Legionellose mit Pneumonie, Pneumonie durch Legionella, Legionella-pneumophila-Infektionen, Legionärskrankheit
Portuguese Doença do legionário, Infecção por Legionella pneumophila, Pneumonia por Legionella, Pneumonia a legionela, Doença dos Legionários, Infecções por Legionella pneumophila
Spanish Infección por Legionella pneumophila, Enfermedad de los legionarios, enfermedad de los legionarios (concepto no activo), infección por Legionella pneumophilia, enfermedad de los legionarios (trastorno), enfermedad de los legionarios, infección por Legionella pneumophila (trastorno), infección por Legionella pneumophila, neumonía de los legionarios (trastorno), neumonía de los legionarios, neumonía por Legionella, Neumonía por legionella, Enfermedad de los Legionarios, Infecciones por Legionella pneumophila
Japanese レジオネラ・ニューモフィラ感染, レジオネラ症, レジオネラ菌性肺炎, ﾚｼﾞｵﾈﾗｼｮｳ, ﾚｼﾞｵﾈﾗｷﾝｾｲﾊｲｴﾝ, ﾚｼﾞｵﾈﾗﾆｭｰﾓﾌｨﾗｶﾝｾﾝ, 在郷軍人病, レジオネラ肺炎, レジオネラニューモフィーラ感染症, 肺炎-レジオネラ
Swedish Legionärssjuka
Czech legionářská nemoc, Legionářská nemoc, Infekce Legionella pneumophila, Legionelová pneumonie
Finnish Legioonalaistauti
Russian LEGIONEROV BOLEZN', ЛЕГИОНЕРОВ БОЛЕЗНЬ
Korean 리지오넬라병
Croatian LEGIONARSKA BOLEST
Polish Choroba legionistów, Zakażenie Legionella pneumonophila
Hungarian Legionarius-betegség, Legionella pneumophila fertőzés, legionella pneumonia, Legionellosisos pneumonia
Norwegian Legionærsyken, Legionærsykdom, Pontiac-feber
Derived from the NIH UMLS (Unified Medical Language System)

Ontology: Pontiac fever (C0343528)

Concepts Disease or Syndrome (T047)
ICD10 A48.2
SnomedCT 240447002
English Nonpneumonic Legionnaires' disease [Pontiac fever], pontiac fever (diagnosis), Pontiac fever, Pontiac fever (disorder), Legionella pneumophila; infection, nonpneumonic, Pontiac; fever, disease (or disorder); legionnaire's, nonpneumonic, fever; Pontiac, infection; Legionella pneumophila, nonpneumonic
Italian Febbre di Pontiac
Japanese ポンティアック熱, ﾎﾟﾝﾃｨｱｯｸﾈﾂ
German Legionellose ohne Pneumonie [Pontiac-Fieber], Pontiac-Fieber
Czech Pontiacká horečka
Korean 비폐렴성 리지오넬라병[폰티액 열]
Hungarian Pontiac-láz
Dutch Legionella pneumophila; infectie, niet-pneumonisch, Pontiac; koorts, aandoening; legionnair, niet-pneumonisch, infectie; Legionella pneumophila, niet-pneumonisch, koorts; Pontiac, Niet-pneumonische legionairsziekte [Pontiac-koorts], Pontiac-koorts
Spanish fiebre de Pontiac (trastorno), fiebre de Pontiac, Fibre de Pontiac
Portuguese Febre pontiac
French Fièvre de Pontiac
Derived from the NIH UMLS (Unified Medical Language System)

Ontology: Legionella pneumophila antigen (C0369588)

Concepts Immunologic Factor (T129)
SnomedCT 121073003
LNC LP38824-6, MTHU007227
English Legionella pneumophila Antigen, Legionella pneumophila Ag, Legionella Pneumophila Antigen, Legionella pneumophila antigen (substance), Legionella pneumophila antigen
Spanish antígeno de Legionella pneumophila (sustancia), antígeno de Legionella pneumophila
Derived from the NIH UMLS (Unified Medical Language System)

Related Topics in Bacterial Infections

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