Unknown fever (FUO)
Fever may appear as part of a harmless common cold or may be a sign of a serious illness. In some cases, the doctor cannot determine a cause of the fever despite a thorough examination. In the case of fever with no apparent cause of more than 3 weeks in duration with temperatures above 38.3 ° C and unsuccessful standard tests, one speaks in technical terms what is known as “fever of unknown cause" ("Fever of unknown origin", FUO).
Physicians distinguish 4 types of fever of unknown cause: