Fever of Unknown Origin  

❖ *Definition:  

 It is a term best reserved for patient with a fever documented by a health care provider 

& fever has lasted for 3 or more weeks. with temperature > 38 degree C on most day 

and for which cause could not be identified after 3 weeks of evaluation as an 

outpatient or after 1 week of evaluation in hospital.  

❖ *Classification:  

 Fever of unknown origin is classified into following 4 categories :  

1) Classic FUO  

2) Health care associated FUO  

3) Immune deficient FUO  

4) HIV-related FUO  

❖ *CAUSES OF FUO  

 A-Infectious causes:  

✓ Bacterial causes (Salmonella, Brucellosis, meningococcal, TB)  

✓ Sphirochaetal (Leptospirosis, Relapsing fever, Syphillis)  

✓ Parasitic (Bilhaziasis(Katayama fever), Babesiosis ,Malaria)  

✓ Fungal (Blastomycosis , Histoplasmosis, Coccidiodomycosis) 

✓ Ricketsial (,Q fever, Tick borne typhus, Rocky mountain spotted fever)  

✓ Viruses(-CMV,-HIV,-hepatitis)  

✓ Local septic infection (Dental abscess , Subphrenic abscess , Tonsillitis ,Hepatic abscess, 

Mastoiditis)  

✓ Local infection without pus formation(UTI, Diverticulitis, Phlebitis, Regional enteritis)

 

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 B-Non-infectious cause:  

✓ Immunological (Rheumatoid arthritis , Systemic lupus, Behcet disease)  

✓ Neoplastic: (Leukaemia, 

Lymphoma, Wilms tumour)  

✓ Metabolic: (Gout, Porphyria)  

✓ Endocrine: (Thyrotoxicosis , Addisons disease, -serum sickness)  

✓ Miscellaneous: (Liver cirrhosis, Familial mediterannean fever, Sarcaidosis, Whipples 

disease, Factious fever malingering)  

❖ Approach To Fever of Unknown Origin  

 A) History  

 Specifics of the history should include the following:  

✓ Duration and characteristics of the fever (number of spikes per day, timing of the 

temperature elevation, whether the temperature returns to normal or below normal)  

✓ Travel history or exposure to people who have traveled to regions endemic for 

particular diseases (typhoid, malaria, tuberculosis, RMSF)  

✓ Exposure to any animals (cat-scratch disease, rat-bite fever, leptospirosis)  

✓ Exposure to unpasteurized dairy products (brucellosis)  

✓ Presence of rashes, conjunctivitis, mucous membrane changes, and arthritis (juvenile 

arthritis, Kawasaki syndrome, SLE)  

✓ Presence of associated cough, weight loss, or lymphadenopathy (lymphoma, 

leukemia, neuroblastoma)  

 B) Physical Examination  

✓ Rectal temperature, respiratory rate, heart rate, and blood pressure measurements 

should be obtained. 

✓ Inspection of the pharynx for hyperemia and exudate, of the tympanic membranes for 

chronic otitis media, and auscultation of the chest for localized wheezing are all 

important.  

✓ In the older child, an examination of the teeth to exclude dental caries and periodontal 

disease should be included. A new cardiac murmur may be a clue to rheumatic fever or 

infective endocarditis.  

✓ Lymphadenopathy, especially if generalized, may suggest a viral infection, such as 

infectious mononucleosis, cytomegalovirus infection, toxoplasmosis, or HIV infection.  

✓ Joints must be examined meticulously for swelling, restricted range of motion, and 

tenderness. Skin rashes may suggest a viral disease or an autoimmune disease such as 

juvenile idiopathic arthritis.  

N.B. Fever with eosinophilia: ( Katayma fever ,fashiolasis 

,trichinosis ,filariasis ,hydatid disease)