A 16-year-old previously healthy boy presents to the emergency department in the summer with 6 days of high fevers, myalgias, arthralgias, anorexia, and fatigue and 1 day of headache and emesis. The fevers have occurred daily, with temperatures as high as 104.5°F (40.3°C), and are associated with chills. The patient has complained of diffuse symmetrical myalgias and arthralgias without joint warmth, edema, or redness. Although the patient experienced transient improvement with acetaminophen and ibuprofen, symptoms have overall progressively worsened.

The patient lives in a wooded area of Missouri and recalls many insect bites. Three weeks before presentation he was bitten by a tick, which he promptly removed. A month earlier the patient returned from a 2-week trip across the Midwest during which he hiked, camped, swam in freshwater rivers and lakes, and was exposed to bats while caving. The family has a pet cat and dog, but he has no...

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