A 32-year-old man comes to the emergency department with a 6-day history of fever, chills, pleuritic chest pain, and a productive cough with streaks of blood. He reports recent intravenous heroin use using nonsterile needles. He also notes progressive fatigue and mild shortness of breath. On examination, his temperature is 39.2°C (102.6°F), pulse 120/min, and blood pressure 112/68 mm Hg. He appears ill. Multiple needle tracks are seen on both forearms. Cardiac examination reveals a holosystolic murmur best heard at the lower left sternal border that increases with inspiration. Lung examination reveals scattered crackles bilaterally. There is no peripheral edema or splenomegaly. Chest x-ray shows multiple bilateral, round nodular infiltrates with some cavitation. ECG shows sinus tachycardia. Three sets of blood cultures drawn before antibiotics are positive for Staphylococcus aureus.