Workup for Febrile 18-Day-Old Infant
This 18-day-old febrile neonate requires a complete sepsis workup including urinalysis with urine culture (catheterized specimen), complete blood count with differential, blood culture, and lumbar puncture for CSF analysis and culture, followed by empiric antibiotic therapy and hospital admission. 1
Rationale for Complete Sepsis Evaluation
Age-Specific Risk Profile
- Neonates under 28 days of age are at highest risk for invasive bacterial infections, with delayed diagnosis associated with increased morbidity and mortality. 2
- The overall incidence of serious bacterial infections in febrile neonates is approximately 16%, with bacteremia and/or meningitis occurring in 4.4% of cases. 3
- Even well-appearing febrile neonates can harbor serious bacterial infections that are not clinically apparent on physical examination alone. 4
Required Diagnostic Components
Urinalysis and Urine Culture (Catheterized Specimen)
- Urinary tract infections are the most common serious bacterial infection in febrile infants, occurring in 8-13% of young febrile infants. 1
- A catheterized specimen is essential—bag urine specimens are unreliable for diagnosis. 1
- Both urinalysis and culture are necessary to distinguish true UTI from asymptomatic bacteriuria. 1
Complete Blood Count with Differential and Blood Culture
- CBC with differential and blood culture (obtained before antibiotics) are recommended for all febrile infants. 1
- Blood cultures must be obtained before antibiotic administration, as giving antibiotics first may obscure the diagnosis. 1
- A normal WBC count does not rule out bacterial infection, especially in neonates. 1
Lumbar Puncture for CSF Analysis and Culture
- Lumbar puncture is specifically recommended for febrile neonates aged 0-28 days. 1
- At 18 days of age, this infant falls squarely within the highest-risk category where meningitis must be excluded, as bacterial meningitis carries significant mortality and neurologic sequelae if missed. 4
- The evaluation of febrile young infants may include lumbar puncture based on clinical factors, but for neonates under 28 days, this is standard practice. 2
Inflammatory Markers
- CRP and procalcitonin are recommended as part of the evaluation for febrile infants. 1
- These markers help risk-stratify patients and guide antibiotic decisions. 2
Why Other Options Are Inadequate
Option A (Admit for observation only): Observation without diagnostic workup is inappropriate for a neonate under 28 days with documented fever, as this age group has the highest risk of serious bacterial infection and cannot be safely observed without first excluding life-threatening infections. 2, 4
Option B (CBC, CMP, blood culture, urinalysis only): This omits the critical lumbar puncture, which is specifically recommended for neonates 0-28 days of age to exclude bacterial meningitis—a potentially fatal condition. 1
Option D (Reassure and discharge): Discharging a febrile neonate without any workup is dangerous and contradicts all current guidelines, as approximately 16% of febrile neonates have serious bacterial infections. 3
Clinical Pitfalls to Avoid
- Do not assume well appearance excludes serious bacterial infection—neonates can appear well despite bacteremia or early meningitis. 4
- Do not administer antibiotics before obtaining cultures, as this obscures diagnostic accuracy. 1
- Do not rely on physical examination alone in neonates under 28 days—the threshold for full sepsis workup is appropriately low in this age group. 2
- Do not use bag urine specimens—only catheterized specimens are acceptable for diagnosis. 1
Post-Workup Management
After completing the full sepsis workup, empiric antibiotic therapy should be initiated and the infant admitted for hospital observation pending culture results. 2, 1 The specific antibiotic regimen should cover common neonatal pathogens including Group B Streptococcus, E. coli, and Listeria monocytogenes.