Fever of Unknown Origin: An Overview of the Diagnostic Approach

Although fever of unknown origin (FUO) was first defined in 1961, it remains a diagnostic challenge. The revised 1991 definition categorized FUO into classic FUO, nosocomial FUO, neutropenic FUO, and human immunodeficiency virus-related FUO, each requiring at least three outpatient visits or 3 days of in-hospital stay. The causes of classic FUO differ greatly geographically and temporally, and are divided into infections, noninfectious...