Legionella (Legionnaires' Disease)
Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management
Definition
Legionnaires' disease is a severe form of pneumonia caused by Legionella pneumophila, often linked to contaminated water systems.
Aetiology
- Caused by Legionella pneumophila, a Gram-negative bacillus.
- Transmission occurs via inhalation of aerosolised contaminated water (e.g., air conditioning, hot tubs, cooling towers).
- No human to human transmission.
Pathophysiology
- Legionella bacteria invade alveolar macrophages and disrupt immune function.
- Leads to severe pneumonia with systemic inflammatory response.
- Exotoxins and endotoxins contribute to cellular damage and multisystem involvement.
Risk Factors
- Age >50 years.
- Smoking and chronic lung disease.
- Immunosuppression (HIV, chemotherapy, corticosteroid use).
- Recent travel with hotel or hospital stays.
- Exposure to contaminated water sources.
Signs and Symptoms
- Fever, chills, and rigors.
- Dry cough progressing to productive cough.
- Dyspnoea.
- Gastrointestinal symptoms: nausea, vomiting, diarrhoea.
- Neurological symptoms: confusion, headache.
- Hyponatraemia and elevated liver enzymes are common.
Investigations
- Chest X-ray: patchy consolidation or lobar pneumonia.
- Urinary Legionella antigen test: rapid and specific.
- Sputum culture: requires special media (BCYE agar).
- Full blood count (FBC): leukocytosis may be present.
- Urea and electrolytes (U&E): may show hyponatraemia.
- Liver function tests (LFTs): often mildly elevated.
Management
1. Antibiotic Therapy:
- First-line: macrolides (azithromycin, clarithromycin) or fluoroquinolones (levofloxacin).
- Severe cases may require IV antibiotics.
2. Supportive Care:
- Oxygen therapy for respiratory distress.
- Fluid management to correct dehydration and electrolyte imbalances.
- Antipyretics for fever.
3. Prevention:
- Proper maintenance of water systems.
- Regular chlorination of water sources.
4. Referral:
- Respiratory medicine: for severe pneumonia or complications.
- Infectious diseases: if prolonged or atypical cases occur.