Fever of unknown origin (FUO) refers to a condition in which the patient has an elevated temperature (fever) but, despite investigations by one or more qualified physicians, no explanation is found.[1][2][3]
If the cause is found it is usually a diagnosis of exclusion, eliminating all possibilities until only the correct explanation remains.
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Mandell's Principles and Practices of Infection Diseases 6th Edition (2004) by Gerald L. Mandell MD, MACP, John E. Bennett MD, Raphael Dolin MD, ISBN0-443-06643-4 · Hardback · 4016 Pages Churchill Livingstone