Signs and Symptoms of Legionnaires' Disease
Legionnaires' disease presents with a constellation of respiratory and extrapulmonary manifestations, including high fever, nonproductive cough, dyspnea, myalgia, gastrointestinal symptoms, and neurological manifestations.
Clinical Presentation
Respiratory Symptoms
- Nonproductive cough
- Dyspnea (shortness of breath)
- Chest pain
- Hypoxemia
- Progression from patchy bronchopneumonia to lobar and multilobar consolidation 1
Systemic Symptoms
- High fever (often >39.4°C/103°F)
- Recurrent chills
- Severe malaise
- Myalgia (muscle pain)
- Headache
- Relative bradycardia (pulse-temperature dissociation) 2
- Acute weight loss 3
Gastrointestinal Manifestations
Neurological Manifestations
- Confusion
- Encephalopathy
- Headache
- Other CNS manifestations 3
Laboratory Abnormalities
- Hyponatremia (low sodium levels)
- Elevated lactate dehydrogenase (LDH) levels
- Microscopic hematuria
- Liver function abnormalities
- Leukocytosis
- Elevated inflammatory markers 3, 2
Severe Complications
Respiratory Complications
Renal Complications
- Acute kidney failure
- Microscopic hematuria 4
Musculoskeletal Complications
- Rhabdomyolysis (breakdown of muscle tissue) 4
Risk Factors for Legionnaires' Disease
Certain individuals are at higher risk for developing Legionnaires' disease:
- Immunosuppressed patients
- Patients with chronic underlying illnesses (hematologic malignancy, end-stage renal disease)
- Patients with diabetes mellitus
- Patients with chronic lung disease
- Smokers
- Elderly individuals 1
Diagnostic Considerations
It's important to note that Legionnaires' disease cannot be distinguished from other pneumonias based on clinical or radiographic findings alone 1, 3. However, the presence of multiple extrapulmonary manifestations (high fever, hyponatremia, gastrointestinal symptoms, neurological symptoms) should increase clinical suspicion 3, 5.
The diagnosis is typically confirmed through:
- Urinary antigen testing (rapid, detects primarily L. pneumophila serogroup 1)
- Culture of respiratory secretions on selective media (gold standard)
- PCR testing of respiratory specimens 3
Clinical Course
Without appropriate treatment, Legionnaires' disease can progress rapidly. The mortality rate is higher among patients with nosocomial acquisition (40%) compared to community-acquired cases (20%), likely reflecting the increased severity of underlying disease in hospitalized patients 1.
Early recognition of the characteristic pattern of symptoms and prompt initiation of appropriate antibiotics (azithromycin or respiratory fluoroquinolones) are essential for improving outcomes 1, 3.