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Fever of unknown origin in children: Etiology

Debra L Palazzi, MD, MEd
Section Editors
Morven S Edwards, MD
Robert Sundel, MD
Jan E Drutz, MD
Deputy Editor
Mary M Torchia, MD


Fever is a common presenting complaint in children, accounting for nearly one-third of pediatric outpatient visits in the United States [1]. The specific entity of "fever of unknown origin" (FUO), as opposed to a "fever without a source" (FWS), has occupied a special place within infectious diseases since the first definition of and series about FUO by Petersdorf and Beeson in 1961 [2]. Although the original definition has been modified, the assessment of broad categories of illness (including infections, connective tissue disease, and malignancy) as a cause of FUO remains useful.

Common etiologies of FUO in children will be discussed below. The approach to the child with FUO, FWS, and fever in unique host groups (eg, newborns, neutropenic children, or those with human immunodeficiency virus [HIV] infection) are discussed separately. (See "Fever of unknown origin in children: Evaluation" and "Fever without a source in children 3 to 36 months of age".)


We apply the term fever of unknown origin (FUO) to children with fever >38.3ºC (101ºF) of at least eight days' duration, in whom no diagnosis is apparent after initial outpatient or hospital evaluation that includes a careful history and physical examination and initial laboratory assessment. (See "Fever of unknown origin in children: Evaluation", section on 'Definitions'.)


The number of infectious and noninfectious etiologies of fever of unknown origin (FUO) in children is extensive (table 1). FUO is usually caused by common disorders, often with an unusual presentation [3-13].

The three most common etiologic categories of FUO in children in order of frequency are infectious diseases, connective tissue diseases, and neoplasms [3-14]. In addition, there are causes of FUO, such as drug fever, factitious fever, central nervous system dysfunction, and others, that do not fit into the above categories. In many cases, a definitive diagnosis is never established and fever resolves.

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Literature review current through: Dec 2017. | This topic last updated: May 26, 2017.
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