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Psittacosis — RACP Adult Medicine MCQ

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ModerateInfectious DiseasesPsittacosisRACP Adult Medicine

A 50-year-old man presents with a 2-week history of productive cough, low-grade fever, and weight loss. He keeps pet birds (budgerigars). CXR shows bilateral lower lobe consolidation. Routine sputum cultures show no growth. His WCC is mildly elevated and LFTs show a hepatitic pattern. What is the most likely diagnosis?

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Correct answer: C — Legionella pneumonia

Psittacosis (caused by Chlamydia psittaci, acquired from birds – particularly parrots, budgerigars, and pigeons) presents with atypical pneumonia (dry or mildly productive cough, headache, fever) with hepatosplenomegaly and a hepatitic picture on LFTs. Splenomegaly is a useful distinguishing feature. Chest X-ray typically shows lower lobe consolidation. Diagnosis is by serology (complement fixation or microimmunofluorescence) or PCR. Treatment is doxycycline 100 mg BD for 14–21 days. It is a notifiable disease in Australia. Macrolides are an alternative for doxycycline-intolerant patients.

Reference: eTG – 2025 – Antibiotic Guidelines; CDNA – 2024 – Psittacosis Guidelines