ABSTRACT
DEFINITIONS Classic Fever of Unknown Origin (FUO) ■ Illness of at least 3 weeks’ duration ■ Temperature >101°F (38.3°C) on several occasions ■ No diagnosis after 1 week in hospital*
Nosocomial FUO* ■ Temperature ≥101°F on several occasions in a hospitalized
patient receiving acute care
Neutropenic FUO* ■ Temperature ≥101°F on several occasions ■ Neutrophils in peripheral blood <0.5 × 109/L (<500/mm3) or
expected to decrease to <0.5 × 109/L within 1-2 days
HIV-associated FUO* ■ Temperature ≥101°F on several occasions in person with
serologically confirmed HIV infection
IS THE PATIENT’S LIFE AT RISK? ■ Immediate mortality for FUO is low, but some patients have
underlying diseases that are ultimately fatal. ■ Three most common causes of FUO are the following:
▲ Infection (30%-40%) ▲ Malignancy (20%-30%) ▲ Collagen vascular disease (10%-20%)
infection or neutropenia. ■ Consider age-visual disturbances with headache in person
>50 years may indicate giant cell arteritis. ■ Evaluate for signs of dehydration, especially with persist-
ent fever and decreased oral intake. ■ Subtle behavioral changes may indicate central nervous sys-
tem infection; perform a thorough neurologic exam.
