Review Question - QID 214862

A 24-year-old man presents to the emergency department for a rash. It started yesterday and has been gradually worsening. He recently had a runny nose after working at an agriculture site and took some penicillin he had left over from a previous infection but otherwise feels well. He has no other medical history and takes no medications. He is studying environmental engineering at his local college. He drinks alcohol socially, does not smoke, and does not use other illicit drugs. His temperature is 97.5°F (36.4°C), blood pressure is 120/72 mmHg, pulse is 68/min, respirations are 15/min, and oxygen saturation is 99% on room air. Physical exam reveals the finding shown in Figure A. Which of the following is the most likely etiology of this patient’s rash?