Legionella

Exam Cram

• Legionnaire's pneumonia is caused by legionella pneumonia, which grows in standing warm water, e.g. hotels water tanks

• Presentation: dry cough, diarrhoea, recent holiday to Spain; CXR consolidation

• Diagnosis: legionella urinary antigen

• Management: Azithromycin or levofloxacin

Outline

Background 

• Outbreaks in lukewarm water tanks

Assessment

History:

• Travel to a foreign hotel

• Shortness of breath, dry cough

• Diarrhoea

Examination:

• Chest auscultation: crackles

• Dehydration

• Febrile

Investigations

• Urinary legionella antigen

• CXR- consolidation

• Hyponatraemia

• Abnormal LFTs

• Blood cultures, repiratory PCR

Diagnosis

Diagnostic criteria: urinary PCR in the context of pneumonia

Management

Acute

1. Azithromycin or clarithromycin

2. Levofloxacin

Med Reg notes

Atypical pneumonia

Legionella is commonly referred to as an 'atypical pneumonia, defined from its inability to be grown in a 'typical' blood culture. It isn't a great term as Legionella is a relatively common cause and the term is going out of fashion. 

The Roman Legion

To help remember the disease, I picture a Roman Legion getting legionnaire's whilst staying in a Spanish hotel!

Management

1. Macrolide, e.g. azithromycin or clarithromycin

2. Fluoroquinolones e.g. levofloxacin

3. Rifampicin

MCQs prefer levofloxacin to erythromycin!

References and Resources

Written in 2025