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A. Fever without localizing symptoms, rash or lymphadenopathy

ii. Those with fever beyond 3 weeks (FUO)

Definition: Fever of unknown origin (FUO) is a term applied to a febrile illness with temperatures exceeding >101?F (38.3?C) that is at least 3 weeks' duration and remains undiagnosed after 3 days in the hospital or after 3 outpatient visits. This is further categorized into:

1.    Neutropenic (neutrophils </= 500): check for perianal, periodontal infections and candidemia, aspergillosis.

2.    HIV associated: mycobacterium avium, mycobacterium TB, non-Hodgkin's lymphoma, drug fever and CMV.

3.    Nosocomial FUO: septic thrombophlebitis, clostridium difficile colitis and drug fever.

4.    Classic FUO: infections, malignancies, inflammatory diseases and drug fever.

a.    Infections: account for 1/3 of the causes.

Abscesses account for 1/3 of the causes. Most of these are intra-abdominal as abscesses, abscesses elsewhere are easily diagnosed.

Mycobacterial infections.

CMV, EBV in the young.

Lower urinary tract infections.

Endovascular infections: infective endocarditis, mycotic aneurysms, infected atherosclerotic plaques.

b.    Malignancy: accounts for 1/3 of the causes. Leukemia and hypernephroma releases endogenous pyrogens. Hepatocellular carcinoma and liver metastasis can also present with fever. Atrial myxoma.

c.    Collagen vascular diseases: account for 10%. SLE is an uncommon cause as it is readily diagnosed serologically.

d.    Granulomatous disease without defined etiology (e.g. sarcoidosis).

e.    Miscellaneous: Crohn's disease, familial Mediterranean fever, hypertriglyceridemia, drug related and recurrent pulmonary embolism.

f.    Factitious:

1. Thermometer in the tea cup routine.

2. Self-injection with pyrogenic containing substances.

3. Injection of medication known by the patient to cause fever.

g.    Undiagnosed.

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