Legionella (Legionnaires' Disease)

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | References

Definition

Legionnaires' disease is a severe form of pneumonia caused by the bacterium Legionella pneumophila. It is typically contracted by inhaling water droplets contaminated with the bacteria.

Aetiology

Legionnaires' disease is caused by Legionella pneumophila, a Gram-negative bacterium commonly found in freshwater environments. The bacteria thrive in warm water systems, such as cooling towers, hot tubs, and large plumbing systems.

Pathophysiology

The pathophysiology of Legionnaires' disease involves:

• Inhalation of aerosolised water droplets containing Legionella bacteria.
• The bacteria enter the lungs and are engulfed by alveolar macrophages.
• Legionella multiplies within the macrophages, causing cell death and subsequent release of the bacteria into the lung tissue.
• This leads to a severe inflammatory response and pneumonia.

Risk Factors

• Age over 50 years
• Smoking
• Chronic lung disease
• Weakened immune system (e.g., due to HIV/AIDS, cancer, or immunosuppressive therapy)
• Recent travel, especially with hotel stays
• Exposure to contaminated water sources (e.g., hot tubs, cooling towers)

Signs and Symptoms

Legionnaires' disease typically presents with:

• High fever
• Chills
• Cough (which may produce sputum)
• Shortness of breath
• Muscle aches
• Headache
• Confusion
• Gastrointestinal symptoms (e.g., nausea, vomiting, diarrhoea)

Investigations

Specific investigations to diagnose Legionnaires' disease include:

• Urinary antigen test: Detection of Legionella antigens in urine.
• Sputum culture: Isolation of Legionella pneumophila from sputum or other respiratory samples.
• Polymerase Chain Reaction (PCR): Detection of Legionella DNA in respiratory samples.
• Chest X-ray: To confirm pneumonia and assess its severity.
• Blood tests: Including full blood count (FBC), liver function tests (LFTs), and renal function tests to assess the overall health status of the patient.

Management

Primary Care Management

• Antibiotics: Macrolides (e.g., azithromycin/clarithromycin) or fluoroquinolones (e.g., levofloxacin) are the antibiotics of choice for treating Legionnaires' disease.
• Supportive care: Ensuring adequate hydration, rest, and monitoring of symptoms.
• Education: Advising on prevention measures, particularly for at-risk individuals and during travel.

Specialist Management

• Hospitalisation: For severe cases or patients with significant comorbidities. This may include oxygen therapy, intravenous antibiotics, and intensive care support.
• Advanced care: Management of complications such as respiratory failure, sepsis, or multi-organ failure.
• Public health measures: Reporting cases to public health authorities and investigating potential sources of contamination to prevent outbreaks.

References

1. NHS (2024) Legionnaires' disease. Available at: https://www.nhs.uk/conditions/legionnaires-disease/ (Accessed: 24 June 2024).
2. Centers for Disease Control and Prevention (2024) Legionella (Legionnaires' Disease and Pontiac Fever). Available at: https://www.cdc.gov/legionella/index.html (Accessed: 24 June 2024).
3. World Health Organization (2024) Legionellosis. Available at: https://www.who.int/news-room/fact-sheets/detail/legionellosis (Accessed: 24 June 2024).
4. British Medical Journal (2024) Legionnaires' disease: clinical features, diagnosis, and management. Available at: https://www.bmj.com/content/351/bmj.h3860 (Accessed: 24 June 2024).

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