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Fever is the most common chief complaint of children presenting to the ED, accounting for ∼30% of pediatric outpatient visits. It is critical to differentiate mildly ill from seriously ill children with fever, especially in the neonate and infant. This challenge is compounded by the nonspecific symptoms and lack of a focus of infection in most children with fever. Many factors influence evaluation and management, including clinical assessment, physical examination findings, patient age, immunization status, and height of the fever.

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This chapter focuses on the management of a neonate, infant, or child with acute fever at risk for serious bacterial illness, because morbidity and mortality are high if not properly treated. Neonates are infants <1 month old. For preterm neonates, the age should be calculated from the date of term birth, rather than from the actual preterm birth date. The significance of age groups is discussed in the subsequent sections.

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Any elevation in temperature above normal is considered a fever, but the threshold for clinically important fever varies with the age group and is related to the ability of signs and symptoms to identify the underlying cause of fever. In the neonate or infant <2 to 3 months of age, the threshold for concerning fever is 38°C (100.4°F); in infants and children 3 to 36 months old, the threshold has traditionally been 39°C (102.2°F).1 In children >36 months old, the definition of significant fever is not fixed because concern for serious bacterial illness in this age group should be directed by other signs or symptoms of the underlying cause. In children with developmental delay, with limited ability to demonstrate specific signs and symptoms, the cause of fever may be difficult to determine, and more testing is often necessary.

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Axillary temperatures are 0.6°C (1°F) lower than oral temperatures, which are 0.6°C (1°F) lower than rectal temperatures. Temperatures taken with infrared thermometers that scan the tympanic membrane are of variable reliability and reproducibility.2

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Fever is treated with acetaminophen or ibuprofen. The dosage of acetaminophen is 15 milligrams/kg/dose (maximum daily dose, 80 milligrams/kg) every 4 to 6 hours, up to five times per day. Acetaminophen can be given PO or PR. The dosage of ibuprofen is 10 milligrams/kg/dose (maximum daily dose, 40 milligrams/kg) every 6 to 8 hours. Ibuprofen can be given PO or IV and is recommended for children older than 1 year of age.

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Infants ≤3 months of age, and especially neonates, are relatively immunodeficient. Neonates and young infants demonstrate decreased opsonin activity, decreased macrophage and neutrophil function, and bone marrow insufficiency.3 Infants and children demonstrate a poor immunoglobulin G antibody response to encapsulated bacteria until 24 months of age. Immune development is a continuum and improves as the child matures. Therefore, the age of the patient and the virulence of the bacteria are considerations for the evaluation of fever in children and the identification of serious bacterial illness. The most common manifestations of serious bacterial illness in children are discussed: urinary tract infection (UTI), bacteremia and sepsis, pneumonia and sinusitis, and meningitis. Of note, the following discussion applies primarily to Western countries.

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Urinary Tract Infection

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Pathophysiology

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Overall, the most common serious bacterial illness is UTI with or without pyelonephritis (see Chapter 128, Urinary ...

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