ABSTRACT
The term fever of unknown origin (FUO) was originally meant to describe perplexing fevers of prolonged duration (1). Petersdorf, in his classic 1961 paper, was the first to define criteria for the diagnosis of FUO. The criteria for classic FUO includes a fever lasting three weeks or more, accompanied by temperatures that are .1018F (38.38C) (2). This definition has been modified over the years to take into account the change in diagnostic modalities and the proportion of patients evaluated for FUO in the ambulatory versus the inpatient setting. Different definitions have been put forward to describe the difference in length of diagnostic workup taking into account the outpatient setting (3-10).
