A fever of unknown origin workup in the emergency department reveals an unusual pathogen

The cause of a fever of unknown origin (FUO, fever of >21 days without an identified etiology) may be a common illness, an atypical presentation of a common illness, or an unusual illness. A patient with an FUO occasionally presents to the emergency department (ED). The differential diagnosis of an FUO is extensive. A primary goal for the ED physician is to determine if the patient with an FUO has a disorder that needs immediate recognition and treatment. We describe a case of a teenage boy who presented to our ED with 2 weeks of high fever and back pain. We describe this teenage boy with FUO and a surprising diagnosis.