Legionella Pneumonia: MRCP Part 2 Notes

The classic picture

Legionella pneumophila causes an atypical pneumonia ("Legionnaires' disease"), typically after exposure to contaminated water systems — air-conditioning, showers, hotels, recent foreign travel.

Features

• Pneumonia — often with relatively few chest signs for the X-ray changes
• Hyponatraemia (a classic clue — SIADH)
• Deranged LFTs, lymphopenia
• Diarrhoea, confusion, relative bradycardia

Diagnosis

• Legionella urinary antigen — rapid first-line (serogroup 1)
• Culture (special media) and PCR confirm
• CXR: patchy consolidation, may progress

Treatment

• Macrolide (clarithromycin/azithromycin) or fluoroquinolone (levofloxacin)
• Beta-lactams do not work — Legionella is intracellular
• Notifiable disease — inform public health (outbreak source control)