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Fever is the most common chief complaint presenting to an emergency department and accounts for 30% of outpatient visits each year. Early studies suggested that infants younger than 3 months were at high risk of a serious bacterial illness (SBI), which included sepsis, pyelonephritis, pneumonia, and meningitis. Current practice guidelines vary in their cut-offs for evaluation and treatment strategies. Neonates are clearly at the highest risk, while infants in their second and third months of life gradually transition to the lower risk profile of older infants and children. The incidence of bacteremia falls from around 10% among febrile neonates to approximately 0.2% in immunized infants and children older than 4 months; meningitis risk decreases from about 1% in the first month of life to < 0.1% later in infancy; the risk for pyelonephritis remains relatively constant among young girls with fever, and gradually decreases among boys over the first year of life. The individual practitioner must weigh these risks against the invasiveness of their ED evaluation and make shared decisions with the family on the best approach.

Clinical Features

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 is 39°C (102.2°F). In general, higher temperatures are associated with a higher incidence of serious bacterial illness.

Young infants are especially problematic in assessing severity of illness. Immature development and immature immunity make reliable examination findings difficult. Persistent crying, inability to console, poor feeding, or temperature instability may be the only findings suggestive of an SBI.

Diagnosis and Differential

Infants Up to 3 Months

History and physical examination are rarely helpful in diagnosing or excluding SBI in this age group as symptoms are typically vague, and physical exam findings are unreliable: meningismus is present in <15% of bacterial meningitis; rales may not be appreciated in the absence of ability to generate negative inspiratory forces; and bacteremia can occur in the well-appearing infant. A history of cough, tachypnea, or hypoxia (by pulse oximetry), however, should alert the examiner to a possible lower respiratory tract infection and prompt chest radiograph.

The safest course for 0 to 28 day old infants is full sepsis testing, admission, and empiric antibiotic treatment. Antibiotic coverage in this age group includes ampicillin for Listeria monocytogenes (see Table 66-1). Sepsis testing includes complete blood count (CBC), blood culture, urinalysis and urine culture, chest radiograph, and lumbar puncture.

Table 66-1 Initial Intravenous Antibiotic Dosages for Bacteremia, Sepsis, and Meningitis

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