Published on June 13, 2017
Fever of unknown origin
A prolonged fever without an established cause despite testing.
Overview
Fever of unknown origin is a prolonged fever without a known cause after testing for common causes. The definition is having a fever higher than 100.9 F on several occasions, fever lasting at least 3 weeks, and an uncertain diagnosis after testing. An infection, a noninfectious inflammatory disease, and cancer are possible causes.