A 37-year-old woman presented with shortness of breath, cough, and fever that began a few days earlier. Her pulse rate was high (110bpm) with a body temperature of 38.6°C. Pulmonary auscultation revealed decreased breath sounds over the lower lung fields. Laboratory study showed pronounced leukocytosis (white cell count of 27,500per cm3) with 89.4% neutrophils and anemia with hemoglobin levels of 9g per dl. Chest X-ray and computed tomography (CT) scan of the chest revealed bilateral pulmonary opacities over the lower lung fields (Fig.