infectious diseases
Fever of Unknown Origin (FUO)
Introduction
Fever of unknown origin (FUO) is body temperature≥38.3°C (≥101° F) rectally that does not result from transient and self-limited illness, rapidly fatal illness, or disorders with clear-cut localizing symptoms or signs or with abnormalities on common tests such as chest x-ray, urinalysis, or blood cultures. FUO is currently classified into 4 distinct categories: Classic FUO:Fever for>3 weeks with no identified cause after 3 days of hospital evaluation or ≥ 3 outpatient visits Health care–associated FUO:Fever in hospitalized patients receiving acute care and with no infection present or incubating at admission if the diagnosis remains uncertain after 3 days of appropriate evaluation Fever in patients with neutropenia and other Overview of Immunodeficiency Disorders if the diagnosis remains uncertain after 3 days of appropriate evaluation, including negative cultures after 48 hours 4 weeks in outpatients with confirmed Human Immunodeficiency Virus (HIV) Infection or 