A Comprehensive Evidence-Based Approach to Fever of Unknown Origin

Abstract

FEVER OF unknown origin (FUO) identifies a syndrome of fever that does not resolve spontaneously, in which the cause remains elusive after an extensive diagnostic workup. Petersdorf and Beeson¹ first coined the term fever of unknown origin in 1961 and explicitly defined it as a temperature higher than 38.3°C on several occasions and lasting longer than 3 weeks, with a diagnosis that remains uncertain after 1 week of investigations in hospital. Petersdorf and Beeson chose 3 weeks of fever to eliminate self-limited viral illnesses and to allow sufficient time for appropriate initial investigations to be completed. Over the past 40 years, health care has shifted from the inpatient to the ambulatory setting. As a result, it has now become widely accepted that the requirement for a 1-week evaluation in hospital be modified so that evaluations may now be completed in an outpatient setting.²