Can Legionella cause lung abscesses?

Legionella as a Cause of Lung Abscess

Yes, Legionella species can cause lung abscesses, particularly in immunocompromised patients, though this is an uncommon manifestation of Legionella infection. 1, 2, 3

Epidemiology and Risk Factors

Legionella lung abscesses are predominantly seen in:

• Immunocompromised patients, especially those receiving corticosteroid therapy for conditions like systemic lupus erythematosus or inflammatory bowel disease 1, 4
• Transplant recipients (particularly bone marrow transplant patients) 1, 5
• Patients with hematologic malignancies or end-stage renal disease 6
• Patients with AIDS or other severe immunodeficiency states 2

Pathophysiology

Legionella lung abscess formation appears to involve:

• Impaired cellular immunity due to underlying conditions or immunosuppressive medications 3
• Neutrophil accumulation in lesions, often during neutrophil recovery phases 3
• Progression from pneumonia to abscess can be rapid, with upper lobes more commonly affected 1

Clinical Presentation

The clinical presentation of Legionella lung abscess may include:

• Symptoms indistinguishable from other causes of pneumonia 6
• Rapidly progressive pneumonia that fails to respond to standard antibiotics 4
• Cavitation on chest imaging that may not be initially present 4

Diagnosis

Diagnosing Legionella lung abscess can be challenging because:

• Legionnaires' disease cannot be distinguished clinically or radiographically from pneumonia caused by other agents 6
• Special culture media are required to isolate Legionella species 2
• Some species like L. micdadei stain weakly Gram-negative and may be confused with mycobacteria due to acid-fast staining properties 2

Recommended diagnostic approaches include:

• Culture of respiratory secretions or tissues on selective media (most specific test) 6
• Urinary antigen testing for L. pneumophila serogroup 1 (rapid but detects only serogroup 1) 6
• Direct fluorescent antibody staining of respiratory specimens 6
• Transthoracic aspiration of abscess cavity contents for culture and PCR 1
• Molecular methods such as PCR on respiratory specimens or abscess material 5

Treatment

For Legionella lung abscess, treatment should include:

• Prompt initiation of appropriate antibiotics with activity against Legionella 1
• Azithromycin or a fluoroquinolone (moxifloxacin, gatifloxacin, levofloxacin) are preferred for hospitalized patients 6
• High-dose erythromycin (4g daily IV) followed by oral therapy for at least 4 weeks has been associated with good outcomes 1
• Ensuring adequate drainage of the abscess cavity, which may require percutaneous catheter drainage or surgical intervention 1, 2
• In some cases, surgical resection may be necessary for cure, particularly in persistent infections 5

Prognosis and Complications

• Mortality rate can be high if not properly diagnosed and treated 1
• Radiologic healing may be slow despite appropriate therapy 1
• Long-term survival without relapse is possible with adequate treatment 1

Important Considerations

• Legionella should be considered early in the differential diagnosis of lung abscess, especially in immunocompromised patients 1
• Mixed infections with other bacteria (like Enterococcus or anaerobes) may occur 4, 5
• Non-L. pneumophila serogroup 1 species (including L. micdadei, L. bozemanii, L. dumoffii, and L. maceachernii) have been isolated from lung abscesses and may be missed by standard urinary antigen testing 3

Prevention

In healthcare settings, prevention of Legionella infections includes:

• Maintaining proper water temperatures (avoiding 25-42°C range that promotes Legionella growth) 6
• Preventing water stagnation in hospital water systems 6
• Regular cleaning to remove scale and sediment that support Legionella growth 6
• Following CDC/HICPAC guidelines for preventing healthcare-associated pneumonia 6