Q. A 40-year-old man comes to the primary care clinic for high fever, chills, a productive cough with yellow sputum, and persistent fatigue over the past week. He reports that despite taking over-the-counter medications, he has not found relief. The patient discloses a history of intravenous drug use. His temperature is 101.5°F (38.6°C), pulse is 110 beats per minute, blood pressure is 120/70 mmHg, and respiratory rate is 14 per minute. Physical examination shows multiple needle track marks from previous intravenous drug use on both arms. Multiple macular, erythematous lesions on the palms and soles and splinter hemorrhages beneath the fingernails are noted. On auscultation, bilateral basal crackles are heard with normal heart sounds. What should be the subsequent diagnostic step for this condition?