What is the appropriate emergency department evaluation for a febrile infant who appears well at 45 days of age?

From the Guidelines

The emergency room work-up for a well-appearing febrile infant at 45 days old should include a full sepsis evaluation, as outlined in the clinical policy for well-appearing infants and children younger than 2 years of age presenting to the emergency department with fever 1. This typically consists of:

• Complete blood count (CBC) with differential
• Blood culture
• Urinalysis and urine culture
• Lumbar puncture for cerebrospinal fluid (CSF) analysis and culture
• Chest X-ray if respiratory symptoms are present After obtaining these tests, empiric antibiotic therapy should be initiated. The recommended regimen is:

• Ampicillin 50 mg/kg IV every 6 hours
• Plus Cefotaxime 50 mg/kg IV every 8 hours (or Ceftriaxone 50 mg/kg IV every 24 hours if Cefotaxime is unavailable) This combination provides broad-spectrum coverage for common pathogens in this age group, including Group B Streptococcus, Escherichia coli, and Listeria monocytogenes, as noted in the revised AAP guideline on UTI in febrile infants and young children 1. The infant should be admitted to the hospital for observation and continued antibiotic therapy pending culture results. Antibiotics can be narrowed or discontinued based on clinical improvement and negative culture results after 36-48 hours, as discussed in the technical report on diagnosis and management of an initial UTI in febrile infants and young children 1. This aggressive approach is necessary because infants in this age group are at high risk for serious bacterial infections, and their immature immune systems may not mount a robust inflammatory response even in the presence of severe infection. The well-appearing nature of the infant cannot reliably exclude serious infection in this age group. Key considerations in the management of febrile infants include the risk of urinary tract infection, which is estimated to be around 5% in this age group, and the importance of early evaluation and treatment to minimize the risk of renal scarring 1.

From the Research

Evaluation of Febrile Infants

The evaluation of febrile infants who appear well at 45 days of age involves several considerations, including the risk of invasive bacterial infection (IBI) and the need for laboratory testing and antibiotic administration.

• The implementation of clinical practice guidelines (CPGs) can expedite care and standardize management, reducing the need for laboratory testing and antibiotic administration in febrile infants aged 0 to 56 days 2.
• For febrile infants aged 30 to 90 days with an abnormal urinalysis, routine lumbar punctures (LPs) may not be necessary if the infant is considered at low risk for serious bacterial infection based on clinical and laboratory criteria 3.
• The Aronson rule, a point-based clinical decision rule, can be used to identify febrile infants ≤60 days of age at low risk of IBI, using variables such as temperature, age, urinalysis, and absolute neutrophil count 4.
• Febrile infants ≤60 days of age with viral infections are at significantly lower, but non-negligible risk for serious bacterial infections (SBIs), including bacteremia and bacterial meningitis 5.
• The Rochester and modified Philadelphia criteria can be used for risk stratification of febrile infants ≤60 days old without routine lumbar puncture, with the modified Philadelphia criteria having higher sensitivity but lower specificity than the Rochester criteria 6.

Laboratory Testing and Antibiotic Administration

• The need for laboratory testing, including complete blood count, blood culture, urine culture, and lumbar puncture, should be determined based on the individual infant's risk factors and clinical presentation 2, 3.
• Antibiotic administration should be guided by the results of laboratory testing and the infant's clinical presentation, with consideration of the risk of IBI and the potential benefits and harms of antibiotic therapy 2, 5.

Risk Stratification

• The risk of IBI and SBI can be stratified using various criteria, including the Aronson rule, the Rochester criteria, and the modified Philadelphia criteria 4, 6.
• Infants who are considered at low risk for IBI and SBI may not require routine lumbar puncture or antibiotic administration, but should be closely monitored for signs of infection and have prompt follow-up evaluation if symptoms persist or worsen 3, 6.