Review Question - QID 108598

A 38-year-old man presents to the emergency department with a 1-week history of fever and nasal congestion that he developed after visiting his sister who has an upper respiratory infection. His past medical history is significant for ongoing IV drug use and obesity. His temperature is 101.8°F (38.8°C), blood pressure is 132/87 mmHg, pulse is 106/min, respirations are 15/min, and SpO2 is 97%. He appears to be in moderate distress. His lungs are clear to auscultation, he has distant cardiac sounds, a 2/6 murmur is noted, and the physical exam finding in Figure A is seen. Two sets of blood cultures drawn 12 hours apart are both positive for Staphylococcus aureus. Which of the following would be necessary to confirm the diagnosis of this patient’s illness?