A 28 year old woman presented with a one week history of increasing shortness of breath on exertion, which was associated with a dry cough and mild pain on the right side of the lateral chest wall. She had also felt feverish and experienced night sweats for three days. Her medical history included mild asthma for five years, which was well controlled on twice daily inhaled beclometasone, and a caesarean section three months before. Her postoperative recovery was uneventful. She was an ex-smoker, rarely drank alcohol, and denied any illicit drug use. In addition, her only recent foreign travel was a trip to France six months ago.

On examination, she was fully alert and oriented but was febrile (38.2°C), with a peripheral oxygen saturation of 95% on room air. On auscultation she had right sided lower zone lung crackles but no wheeze. The lymph nodes were not palpable. Her blood pressure was 96/60 mm Hg and her pulse was 84 beats/min. Initial blood tests showed haemoglobin 127 g/L (reference range 115-165) and the total white cell count 9.3×10⁹/L (4.0-11.0), with an eosinophil count of 2.3×10⁹/L (0.0-0.4). C reactive protein and erythrocyte sedimentation rate were raised at 172 mg/L (<5) and 102 mm in the first hour (0-15), respectively. Renal and liver function tests were normal and HIV serology was negative. A plain posterior-anterior radiograph is shown in fig 1⇓.