What is the treatment for Legionnaires disease?

Treatment of Legionnaires' Disease

For Legionnaires' disease, the preferred treatment is azithromycin or a respiratory fluoroquinolone (levofloxacin, moxifloxacin, or gatifloxacin) for hospitalized patients, while outpatients can be treated with erythromycin, doxycycline, azithromycin, clarithromycin, or a fluoroquinolone. 1

Diagnosis

Before initiating treatment, appropriate diagnostic testing should be performed:

• Preferred diagnostic tests:

  • Urinary antigen assay (detects L. pneumophila serogroup 1, which causes 80-95% of community-acquired cases)
  • Culture of respiratory secretions on selective media 1

• When to test for Legionella:

  • Any patient hospitalized with enigmatic pneumonia
  • Patients with severe pneumonia requiring ICU care
  • Pneumonia in immunocompromised hosts
  • During epidemics
  • Failure to respond to β-lactam antibiotics 1

Treatment Algorithm

For Hospitalized Patients:

1. First-line therapy:

   • Azithromycin OR
   • Respiratory fluoroquinolone (levofloxacin, moxifloxacin, or gatifloxacin) 1, 2

2. Treatment duration:

   • 10-21 days for most antibiotics
   • Shorter course for azithromycin due to its long half-life 1

3. Special considerations:

   • Initiate treatment as rapidly as possible - delay is associated with increased mortality 1
   • For immunocompromised patients, consider longer treatment courses (10-14 days) 3

For Outpatients (Mild Disease):

1. Acceptable antibiotics:

   • Erythromycin
   • Doxycycline
   • Azithromycin
   • Clarithromycin
   • Respiratory fluoroquinolone 1

2. From an antimicrobial stewardship perspective:

   • Monotherapy with doxycycline or a respiratory quinolone provides optimal cost-effective therapy 4

Clinical Considerations

Risk Factors for Legionnaires' Disease:

• Recent travel with overnight stay outside the home
• Exposure to spas
• Recent changes in domestic plumbing
• Renal or hepatic failure
• Diabetes
• Systemic malignancy
• Compromised cell-mediated immunity
• Smoking
• Increasing age 1

Clinical Features:

While no single feature is diagnostic, the following may suggest Legionnaires' disease:

• High fever
• Hyponatremia
• CNS manifestations
• Elevated lactate dehydrogenase levels (>700 U/mL)
• Severe disease 1

Important Caveats

1. Do not wait for diagnostic confirmation:

   • Treatment should be initiated as soon as Legionnaires' disease is suspected
   • Treatment should be given or continued even if Legionella-specific tests are negative when clinical and epidemiological evidence suggests the disease 1

2. Diagnostic limitations:

   • No laboratory test detects all patients with Legionnaires' disease
   • Urinary antigen test is less sensitive for nosocomial cases due to involvement of serogroups other than serogroup 1 1

3. Treatment response:

   • Monitor for clinical improvement
   • Switch from parenteral to oral therapy only after clinical response is observed 5

4. Recent evidence:

   • More recent studies suggest fluoroquinolones (levofloxacin or moxifloxacin) or azithromycin as preferred first-line therapy for Legionnaires' disease 6
   • Levofloxacin is FDA-approved for treatment of community-acquired pneumonia due to Legionella pneumophila 2

By following this treatment approach, you can effectively manage Legionnaires' disease and reduce the risk of mortality, which ranges from 5-25% among immunocompetent hosts 1.