Fever of unknown origin

Pyrexia of unknown origin, febris e causa ignota

Various

Exaggerated [6]

circadian rhythm

Fever higher than 38.3 °C (101 °F) on several occasions

Persisting without diagnosis for at least 3 weeks

At least 1 week's investigation in hospital

Treatment[edit]

Unless the patient is acutely ill, no therapy should be started before the cause has been found. This is because non-specific therapy is rarely effective and may delay the diagnosis. An exception is made for neutropenic (low white blood cell count) patients or patients who are severely immunocompromised in which delay could lead to serious complications.[4] After blood cultures are taken this condition is aggressively treated with broad-spectrum antibiotics. Antibiotics are adjusted according to the results of the cultures taken.[1][2][3]


HIV-infected people with pyrexia and hypoxia will be started on medication for possible Pneumocystis jirovecii infection. Therapy is adjusted after a diagnosis is made.[3]

Prognosis[edit]

Since there is a wide range of conditions associated with FUO, prognosis depends on the particular cause.[1] If after six to twelve months no diagnosis is found, the chances of ever finding a specific cause diminish.[3] Under those circumstances, the prognosis is good.[2]

Chronic fatigue syndrome

Encephalitis lethargica

Idiopathic chronic fatigue

Idiopathic disease