What is the appropriate workup for fever in a 3-month-old (three months old) inpatient?

From the Guidelines

For a 3-month-old infant with fever requiring inpatient workup, a comprehensive evaluation is necessary due to the high risk of serious bacterial infection in this age group, as supported by the clinical policy for well-appearing infants and children younger than 2 years of age presenting to the emergency department with fever 1. The workup should include:

• A complete blood count
• Blood culture
• Urinalysis with culture
• Lumbar puncture for CSF analysis and culture Chest X-ray should be performed if respiratory symptoms are present. Empiric antibiotic therapy should be initiated promptly with ampicillin (50 mg/kg IV every 6 hours) plus gentamicin (4 mg/kg IV every 24 hours) or ampicillin plus cefotaxime (50 mg/kg IV every 8 hours) to cover common pathogens including Group B Streptococcus, Escherichia coli, and Listeria monocytogenes, as recommended by the American College of Emergency Physicians 1. The infant should be closely monitored for vital signs, hydration status, and clinical improvement. Antibiotics should be continued for at least 48-72 hours while awaiting culture results, with therapy adjusted based on these results, to minimize the risk of morbidity and mortality associated with bacterial infections in this age group 1. This aggressive approach is warranted because infants under 3 months have immature immune systems and can rapidly deteriorate with bacterial infections, often presenting with subtle symptoms despite serious illness, and the consequences of missing a bacterial infection can be severe, including meningitis, sepsis, and death.

From the Research

Fever Workup in 3-Month-Old Inpatient

• A sepsis workup for a 3-month-old infant with fever typically includes a complete blood count, blood culture, urine culture, and lumbar puncture, as seen in a case report of a 14-week-old boy with fever 2.
• The management of fever in young infants may differ between general emergency departments and pediatric emergency departments, with pediatric emergency departments being more likely to adhere to consensus guidelines, including performing critical components of initial management such as blood culture, urine culture, and lumbar puncture 3.
• For infants aged 30 to 90 days with a fever and an abnormal urinalysis, a lumbar puncture may not be necessary if the infant is considered at low risk for serious bacterial infection based on clinical and laboratory criteria 4.
• The use of procalcitonin measurement has been studied as a potential tool to guide antibiotic use in children with fever without source, but its impact on antibiotic use is unclear, with one study finding no significant difference in antibiotic use between patients with procalcitonin results revealed to the attending physician and those with results not revealed 5.
• Recent guidelines from the American Academy of Pediatrics provide updates on the evaluation and management of well-appearing febrile infants from age 8 to 60 days, incorporating evidence from the last 20 years and replacing previous varied protocols 6.

Laboratory Tests and Procedures

• Complete blood count: a common test used in the initial evaluation of a febrile infant 2, 3, 5.
• Blood culture: a critical component of the sepsis workup for a febrile infant 2, 3, 5.
• Urine culture: an important test for identifying urinary tract infections in febrile infants 2, 3, 4.
• Lumbar puncture: a procedure that may be necessary for febrile infants with suspected bacterial meningitis or other serious bacterial infections, but may not be necessary for infants with an abnormal urinalysis who are at low risk for serious bacterial infection 2, 3, 4.

Clinical Decision-Making

• Clinical judgment is crucial in determining the need for a lumbar puncture in febrile infants with an abnormal urinalysis 4.
• The use of procalcitonin measurement may not significantly impact antibiotic use in children with fever without source, and its use should be guided by clinical judgment 5.
• Recent guidelines from the American Academy of Pediatrics provide a framework for the evaluation and management of well-appearing febrile infants from age 8 to 60 days, but clinical judgment is still necessary for infants who fall outside of this guideline's scope 6.