Review Question - QID 109285

A 10-year-old girl presents to your office with a fever and rash. Her mother first noticed the rash 2 days ago after a camping trip. The rash began on her wrists and ankles and has now spread to her palms and the soles of her feet. This morning, she was feeling unwell and complaining of a headache. She had a fever of 102°F (39°C) prompting her mother to bring her to your office. She is otherwise healthy and does not take any medications. Her medical history is significant for a broken arm at age 8. On physical exam her blood pressure is 120/80 mmHg, pulse is 110/min, and respirations are 22/min. You notice a petechial rash on the palms, soles, ankles, and wrists. Which of the following findings would confirm the most likely cause of this patient's symptoms?