a 35-year-old patient undergoing initial therapy for acute myeloid leukemia has tolerated the chemotherapy well. however, 6 days after the initiation of chemotherapy and ~10 days after the insertion of an indwelling transthoracic intravenous device (hickman catheter), he develops a fever. examination is negative except for erythema and tenderness at the insertion site and along the subcutaneous tunnel. blood cultures and chest x-ray are negative. the most appropriate course of action at this point is to