Fever of Unknown Origin

This chapter on fever of unknown origin (FUO) begins by clarifying the definition of FUO and continues by listing and describing the major etiologies of FUO, providing guidance on clinical workup and discussing best management practices. Discussion of FUO etiologies emphasizes that most fall under a few categories—rheumatological, infectious, neoplastic, and other. Emergency management of stable, immunocompetent patients with FUO is best when focused on an appropriate diagnostic workup so that a definitive diagnosis can be established and treated with targeted therapy. Antibiotics should not be started in the emergency department for stable, immunocompetent patients with FUO unless the specific etiology is uncovered. This chapter is concise and targeted to the emergency medicine provider who needs to know how best to evaluate and manage the patient with a clinical history consistent with FUO.