Legionellosis – MD Nexus

Epidemiology

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

Microbiology

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

Diagnosis

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

Leukocytosis (see Leukocytosis, [[Leukocytosis]])

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
- Complete Blood Count (CBC) (see Complete Blood Count, [[Complete Blood Count]]): leukocytosis
- Arterial Blood Gas (ABG) (see Arterial Blood Gas, [[Arterial Blood Gas]]): absence of hypoxemia
- Chest X-Ray/Chest CT (see Chest X-Ray, [[Chest X-Ray]] and Chest Computed Tomography, [[Chest Computed Tomography]]): absence of infiltrates
- Bronchoscopic Bronchoalveolar Lavage (BAL) (see Bronchoscopy, [[Bronchoscopy]]): neutrophilia
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

Cardiovascular

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
- Delirium (see Delirium, [[Delirium]])

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

Treatment

Antibiotics

Fluoroquinolones (see Fluoroquinolones, [[Fluoroquinolones]]): effective
xxxx

References

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]