A 32-year-old woman developed a furuncle on her foot 1 week ago. Two days ago, she developed fever, headache, high fever with chills, productive cough with blood-tinged sputum, and chest pain. Auscultation revealed increased breath sounds with occasional fine crackles in both lungs. WBC was 2×10<sup>9</sup>/L with 90% neutrophils. Chest X-ray showed scattered faint round lesions in both lungs, some with cavities containing air-fluid levels. The most likely diagnosis is: