Legionella is a Gram-negative, aerobic bacillus that thrives in aquatic environments and man-made water systems. It requires special culture media (buffered charcoal yeast extract) for growth.

urinary antigen testing (detects L. pneumophila serogroup 1), PCR from respiratory samples, or culture

Legionnaire's disease is caused by the intracellular bacterium Legionella pneumophilia. It 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

Investigations

• diagnositic test of choice:urinary antigen
• chest x-ray findings are non-specific but may include:
  • a mid-to-lower zone predominance of patchy consolidation
  • pleural effusions in around 30%

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%.