<i>Legionella</i>

Microbiology

Legionnaire's disease is caused by the intracellular bacterium Legionella pneumophilia. It is typically colonizes water tanks and hence questions may hint at air-conditioning systems or foreign holidays. Person-to-person transmission is not seen

Features

flu-like symptoms including fever (present in > 95% of patients)
dry cough
relative bradycardia
confusion
lymphopaenia
hyponatraemia
deranged liver function tests
pleural effusion: seen in around 30% of patients

Diagnosis

Urinary antigen (initial)
Sputum culture is considered gold standard

Management

Treatment is typically with a fluoroquinolone, e.g. levofloxacin, or newer macrolide, e.g. azithromycin or clarithromycin. In severely ill patients a fluoroquinolone and macrolide may be used in combination initially.


© Image used on license from Radiopaedia

Chest x-ray features of legionella pnuemonia are non-specific but includes a mid-to-lower zone predominance of patchy consolidation. Pleural effusions are seen in around 30%.