The chapter begins with the definition of fever as a body temperature of 1 °C (1.8 °F) or greater above the mean at the site of temperature recording. For example, the range of body temperature at the axilla is 34.7–37.4 °C, with a mean of 36.4 °C; 1 °C above the mean is 37.4 °C. The following degrees of temperature are accepted as fever: rectal temperature ≥38.0 °C, oral temperature ≥37.6 °C, axillary temperature ≥37.4 °C and tympanic membrane ≥37.6 °C.
Fever arises when macrophages and other cells secrete endogenous pyrogens in response to external pyrogens such as bacteria or viruses. These endogenous pyrogens (also called cytokines), in particular IL-1 and IL-6, act via complicated mechanisms to raise the hypothalamic set points to cause fever.
Fever is an extremely common presentation, most frequently due to self-limited viral infection and sometimes to uncomplicated bacterial infection that resolves within a week. Fever can be a manifestation of a serious underlying disease.
Recurrent fever, relapsing fever and periodic fever syndromes are described with some details. They are now up to date with most recent scientific evidence.
Complications directly related to fever are rare. Dehydration is the most common complication that can easily be treated with extra fluid intake. Morbidity and mortality are closely linked to the severity of the underlying disease and not to the level of fever.
Fever is then divided into three main categories: fever with localized signs, fever without localized signs and persistent fever of unknown cause (PUO). The most common febrile illnesses encountered in paediatric practice belong to fever with localization. In this category, fever is usually of short duration, either because it settles spontaneously after a common viral infection or because a specific treatment, such as an antibiotic, has been administered. Diagnosis is usually suggested by the history and physical examination and confirmed by simple investigation, such as a chest X-ray. As children younger than 36 months experience the highest rate of febrile illnesses with localizing signs, discussion of this subject is added. The two most important causes of fever without localization are urinary tract infection and bacteraemia. Urine specimen should always be submitted for culture in children without localization.
Drug fever and foetal malformation are the final topics in this chapter.
Definitions of fever Periodic and relapsing fevers Auto-inflammatory diseases Fever classifications Drug fever
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