fever of unknown origin
the presence of fever (temperature >101°F or 38.3°C) of unknown cause after intensive investigation. Exact criteria for use of term vary, especially regarding duration of fever and extent of clinical investigation; generally a duration of longer than 1 week (some authors require 2–3 weeks) and thorough inpatient investigation or at least three outpatient visits, including a careful history, physical examination, and laboratory tests such as cultures, serologic studies, and invasive procedures for biopsy and/or culture, as indicated by clinical clues or epidemiologic considerations.
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Examples: glitazone, GI cocktail, etc.