The current criteria for definition of FUO (fever of un- known origin) is that the fever lasting for more than___ weeks.

Ans. c (21 days). (Ref. Harrison's principles of internal medicine 18th ed. Ch. 18).FUO (FEVER OF UNKNOWN ORIGIN)Definition - Fever of unknown origin (FUO) was defined by Petersdorf and Beeson in 1961 as:1) temperatures of >38.3AdegC (>101AdegF) on several occasions;2) a duration of fever of >3 weeks; and3) failure to reach a diagnosis despite 1 week of inpatient investigation.Types - Durack and Street's new classification of FUO:# Classic FUO# Nosocomial FUO# Neutropenic FUO# FUO associated with HIV infectionClassic FUOCorresponds closely to the earlier definition of FUO, differing only with regard to the prior requirement for 1 week's study in the hospital. The newer definition is broader, stipulating three outpatient visits or 3 days in the hospital without elucidation of a cause or 1 week of "intelligent and invasive" ambulatory investigation.Nosocomial FUOa temperature of 38.3degC (lOTF) develops on several occasions in a hospitalized patient who is receiving acute care and in whom infection was not manifest or incubating on admission. Three days of investigation, including at least 2 days' incubation of cultures, is the minimum requirement for this diagnosis.Neutropenic FUODefined as a temperature of 38.3AdegC (101degF) on several occasions in a patient whose neutrophil count is <500/L or is expected to fall to that level in 1-2 days. The diagnosis of neutropenic FUO is invoked if a specific cause is not identified after 3 days of investigation, including at least 2 days' incubation of cultures.HIV-associated FUODefined by a temperature of 38.3AdegC (101degF) on several occasions over a period of >4 weeks for outpatients or >3 days for hospitalized patients with HIV infection. This diagnosis is invoked if appropriate investigations over 3 days, including 2 days' incubation of cultures, reveals no source.Causes of FUOInfections# Infections remain the most common cause of FUO.# Tumors have classically been the second most common cause of FUO in adults.# Tumors that present most often as FUO are hematologic malignancies, especially Hodgkin's disease and other lymphomas (Pel-Ebstein fevers--those that occur daily for days to weeks then disappear, only to reappear later in the same pattern--are now rarely seen), multiple myeloma and leukemias. Solid tumors like renal cell carcinoma is most often noted to cause FUO; much less commonly, hepatomas and cancer of the colon and gastrointestinal tract, lung, and breast, atrial myxomas, can cause FUO.Collagen vascular diseases, granulomatous diseases# Still's disease is the most frequent diagnosis in adults younger than 50 years; in older adults with FUO, temporal arteritis is the most common diagnosis. Other causes of FUO include polyarteritis nodosa, cryoglobulinemia, poly-myositis, Wegener's granulomatosis, and sarcoidosis.Other causes of FUO# Common entities, such as pulmonary emboli and hematomas, can manifest as FUO primarily.# Many different drugs can cause fever (table below), and hyperthyroidism and thyroiditis can also present as FUO.# Periodic fevers, such as familial Mediterranean fever, are rare and occur in select populations.# Factitious and fraudulent fevers--interesting diagnostic dilemmas that appear in every series of FUO--are uncommon.Commonly used medications that can cause fever of unknown originAntimicrobialsAnticonvulsantsAntihistaminesCardiovascular drugs H2-blockersMiscellaneousCarbapenemsCephalosporinsMinocycline HCINitrofurantoinPenicillinsRifampinSulfonamidesBarbituratesCarbamazepinePhenytoinHydralazineProcainamide HCIQuinidineCimetidineRanitidine HCIIodidesHerbal remediesNonsteroidal anti-inflammatory drugsIbuprofenSulindacPhenothiazinesSalicylates