Makindo Medical Notes

Related Subjects:Pneumonia |Pontiac fever (Legionella Pneumophila) |Legionella Pneumophila pneumonia |Asthma |Acute Severe Asthma |Exacerbation of COPD |Pulmonary Embolism |Cardiogenic Pulmonary Oedema |Pneumothorax |Tension Pneumothorax |Respiratory (Chest) infections Pneumonia |Fat embolism |Hyperventilation Syndrome |ARDS |Respiratory Failure |Diabetic Ketoacidosis

💧 Aquatic organisms found in air conditioning, hot water systems, and cooling towers. Because Legionella is an intracellular pathogen, only antibiotics that penetrate cells are effective. Large numbers can be aerosolised from contaminated water → epidemic outbreaks, especially in urban settings.

📖 About

• First identified after an outbreak at an American Legion convention in Philadelphia (1976).
• Causes community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP).
• Also causes Pontiac fever – a milder, self-limiting flu-like illness without pneumonia.
• Penicillins & Cephalosporins ❌ are not effective.

🔬 Characteristics

• Gram-negative, rod-shaped bacillus, intracellular pathogen.
• Obligate aerobe, slow-growing, fastidious.
• Non-motile, non-capsulated, but survives within macrophages.
• Adheres via fimbriae, invades phagocytic cells.
• L. pneumophila serogroup 1 causes most human disease.

👥 Vulnerable Patients

• Those with COPD, CHF, renal, or haematological disease.
• Organ transplant patients, immunosuppressed individuals.
• Fatality rates up to 50% in high-risk groups if untreated.
• Risk ↑ in diabetics, smokers 🚬, alcohol misuse 🍺.

🌍 Source

• Water reservoirs: air conditioning, showers, spas, hot water systems.
• Thrives at 20–45 °C; no human-to-human spread.
• Grows in biofilms and inside amoebae.
• Favourable factors: stagnant water, lukewarm temperatures, biofilm-conducive plumbing.

🤒 Clinical Features

• Legionnaires’ disease (pneumonia): fever, dry cough, headache, myalgia, diarrhoea + confusion 💡 (clues vs other pneumonias).
• Pontiac fever: flu-like illness, non-productive cough, recovery in 2–5 days without antibiotics.
• Can be severe → necrotising pneumonia, respiratory failure.

🧪 Investigations

• Bloods: FBC, U&E, LFTs (often deranged LFTs 🟠 clue).
• Chest X-ray: patchy or lobar pneumonia.
• Culture: Buffered Charcoal Yeast Extract (BCYE) agar (3–5 days).
• Rapid tests: Urinary antigen (serogroup 1), PCR.
• Serology (4-fold antibody rise) for retrospective confirmation.

💊 Management

• Supportive care: Oxygen, fluids, ITU/HDU support if severe.
• Antibiotics (10–21 days):
  • Macrolides: Azithromycin, Clarithromycin, Erythromycin.
  • Fluoroquinolones: Levofloxacin, Ciprofloxacin.
  • Doxycycline also effective.
• Pontiac fever: No antibiotics needed ✅.

🛡️ Prevention

• Hyperchlorination & superheating of water systems (>70 °C).
• Regular maintenance of air conditioning & hot water systems.
• Monitoring water quality and biofilm control.

📚 References

• Review article
• CDC – Legionella