Severe Legionella pneumonia — FFICM MCQ

Correct answer: D — Legionella pneumophila pneumonia

The correct answer is D, Legionella pneumophila pneumonia. The combination of severe pneumonia acquired after recent hotel or travel exposure, with prominent diarrhoea, confusion, hyponatraemia (sodium 124 mmol/L) and deranged liver enzymes, is the classic multisystem pattern of legionellosis rather than a simple bacterial or viral pneumonia. Legionella colonises water systems such as hotel air conditioning, showers and cooling towers, explaining the epidemiological link, and its systemic toxin effects account for the extrapulmonary features (gut, CNS, liver, syndrome of inappropriate antidiuretic hormone secretion causing hyponatraemia). Gram stain showing neutrophils but no dominant organism fits an atypical pathogen that does not stain or culture on routine media, consistent with current UK guidance that atypical cover (macrolide or quinolone) should be added in severe community acquired pneumonia and that urinary antigen testing be sent. Why the other options are wrong: B Pneumocystis jirovecii pneumonia: occurs in immunocompromised (typically HIV, low CD4) patients, causes a dry cough with exertional hypoxia and diffuse interstitial changes, not the multisystem sodium/liver/GI picture described. C Aspiration pneumonitis: would show a history of impaired swallow or reduced consciousness prior to the pneumonia and typically affects dependent lung zones, without hyponatraemia, diarrhoea or hepatic derangement as core features. D Staphylococcus aureus pneumonia: usually follows influenza, shows cavitating or necrotising changes and would be expected to reveal clustered Gram-positive cocci on sputum Gram stain, not a non-diagnostic stain. E Pulmonary oedema: is a non-infective cause of bilateral shadowing and would not produce neutrophilic sputum, diarrhoea, hyponatraemia or deranged liver enzymes. Key point: hotel or travel-associated severe pneumonia with hyponatraemia, diarrhoea, confusion and abnormal liver function is the classic multisystem clue to Legionella, prompting urinary antigen testing and macrolide or quinolone atypical cover.

Reference: NICE Guideline NG250, Pneumonia: diagnosis and management (2025), Recommendations on investigations and antibiotic choice in moderate to high severity community-acquired pneumonia, nice.org.uk/guidance/ng250