You are answering a USMLE-style medical question. Question: A 43-year-old man with a history of hepatitis C and current intravenous drug use presents with 5 days of fever, chills, headache, and severe back pain. On physical exam, temperature is 100.6 deg F (38.1 deg C), blood pressure is 109/56 mmHg, pulse is 94/min, and respirations are 18/min. He is thin and diaphoretic with pinpoint pupils, poor dentition, and track marks on his arms and legs. A high-pitched systolic murmur is heard, loudest in the left sternal border and with inspiration. He is admitted to the hospital and started on broad-spectrum antibiotics. One of the blood cultures drawn 12 hours ago returns positive for Staphylococcus aureus. Which of the following is the most appropriate next step to confirm the diagnosis? Options: A) Repeat blood cultures now B) Repeat blood cultures 24 hours after initial cultures were drawn C) Repeat blood cultures 48 hours after initial cultures were drawn D) Do not repeat blood cultures Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.