A 32-year-old woman presents to the emergency department complaining of a 10-day history of daily high fevers, severe joint pain, and a transient skin rash. She notes that her temperature spikes typically occur in the late afternoon, accompanied by a pinkish rash on her trunk that fades as her fever subsides. She also reports a severe sore throat and generalized muscle aches that make it difficult to get out of bed. She describes her joint pain as “excruciating,” primarily affecting her wrists, knees, and ankles. She has no significant past medical history and takes no daily medications. She denies recent travel, tick bites, or sick contacts.

She appears highly distressed and diaphoretic. She is febrile with a temperature of 39.6°C. Her blood pressure is 112/72 mmHg, with a bounding heart rate of 118 bpm and a respiratory rate of 18 breaths per minute. Her lungs are clear to auscultation bilaterally. Her cardiac exam shows a regular rhythm with no murmurs or rubs. Her abdomen is soft and non-tender, with a palpable liver edge 2 cm below the costal margin.