BACKGROUND: Epidemiological changes and the ongoing expansion of the diagnostic armamentarium warrant a regular update of the spectrum of diseases that present as prolonged febrile illnesses. METHODS: We prospectively collected a series of 290 immunocompetent @entity1 referred to our university hospital between 1990 and 1999 with a @entity221 (temperature >38.3 degrees C) of uncertain cause, lasting at least 3 weeks. @entity1 were categorized in 4 groups according to the timing of diagnosis: early diagnosis (within 3 in-hospital days or 3 outpatient visits), intermediate diagnosis (between days 4 and 7), late diagnosis (after day 7), and no diagnosis during index contact or follow-up. RESULTS: A final diagnosis was established early in 67 @entity1 (23.1%), intermediate in 38 (13.1%), and late in 87 (30.0%). In the remaining 98 (33.8%), no diagnosis was made. The cause of the @entity221 remained obscure in 50 (47.6%) of 105 @entity1 with episodic @entity221 vs 48 (25.9%) of 185 @entity1 with continuous @entity221 (P<.001). Among the 192 @entity1 with a final diagnosis, noninfectious inflammatory diseases represented the most prevalent diagnostic category (35.4%), surpassing infections (29.7%), miscellaneous causes (19.8%), and @entity5 (15.1%). Fourteen disorders accounted for over 59% of diagnoses, whether diagnosis was reached early, intermediate, or late. @entity1583 made up 11.5% of diagnoses, but were responsible for 14 (58.3%) of the 24 fatalities related to the @entity221 . Of the 80 @entity1 discharged alive without diagnosis and for whom follow-up was available, 3 died, but the @entity204 were considered to be unrelated to the feverish illness. CONCLUSIONS: Prolonged febrile illnesses remain a diagnostic challenge. Despite the technological progress of the late 20th century, the origin of the @entity221 remains elusive in many @entity1 , especially in those with episodic fevers. Noninfectious inflammatory diseases emerge as the most prevalent diagnostic category.

From prolonged XXXX to @entity221 of unknown origin: the challenge continues.

@entity1 :: ('9606', 'Species') :: ['Patients', 'patients'] @entity5 :: ('MESH:D009369', 'Disease') :: ['malignancies'] @entity1583 :: ('MESH:D019337', 'Disease') :: ['Hematological malignancies'] @entity204 :: ('MESH:D003643', 'Disease') :: ['deaths'] @entity221 :: ('MESH:D005334', 'Disease') :: ['febrile illness', 'fever']
@entity221 :: (MESH:D005334,Disease) :: ['febrile illness']
