What are the next steps for a baby with a vacillating fever, constipation, and spit up?

Management of a Well-Appearing Febrile Infant Under 28 Days

This infant requires immediate comprehensive evaluation including urinalysis with urine culture, complete blood count with differential, blood culture, inflammatory markers, lumbar puncture, empiric parenteral antibiotics, and hospitalization. 1

Age-Based Risk Assessment

This infant appears to be under 28 days old based on the clinical context, placing them in the highest-risk category for serious bacterial infections (SBI):

• Infants under 28 days have an 8-13% incidence of SBI, making aggressive evaluation mandatory regardless of clinical appearance 1
• Approximately 58% of infants with bacteremia or bacterial meningitis appear clinically well, so the reassuring examination does not exclude serious infection 1
• The risk of bacterial meningitis is approximately 0.5% in this age group, but missed diagnosis leads to permanent neurologic sequelae and death 1

Mandatory Diagnostic Workup

Urine Studies

• Obtain urinalysis and urine culture via catheterization or suprapubic aspiration - never use a collection bag as this dramatically increases false-positive results 1
• Urinary tract infection is the most common SBI in febrile infants, with prevalence of 5-7% in infants younger than 24 months 1
• In the post-pneumococcal vaccine era, E. coli causes 87.4% of UTIs and 60% of bacteremia in young infants 2

Blood Work

• Complete blood count with differential to assess WBC count and absolute neutrophil count 1
• Blood culture must be obtained before initiating antibiotics 1
• Inflammatory markers (C-reactive protein) as part of initial evaluation 1

Lumbar Puncture

• All infants under 28 days with fever require lumbar puncture to exclude bacterial meningitis, regardless of clinical appearance 1, 2
• Never delay lumbar puncture based on "low-risk" clinical criteria, as these criteria do not apply to infants under 28 days 1

Chest Radiograph

• Not indicated unless respiratory signs or symptoms are present (cough, hypoxia, rales, tachypnea out of proportion to fever) 2, 1
• The prevalence of pneumonia in febrile infants up to 3 months is low (1-3%) 1

Empiric Antibiotic Therapy

For infants 8-21 days old with no focus identified:

• Ampicillin IV or IM (150 mg/kg per day divided every 8 hours) AND
• Either ceftazidime IV or IM (150 mg/kg per day divided every 8 hours) OR gentamicin IV or IM (4 mg/kg per dose every 24 hours) 2

Antibiotics must be initiated immediately after cultures are obtained given the high risk of SBI in this age group 1

Hospitalization

• Mandatory for all infants under 28 days with fever 1
• Hospital monitoring allows for careful observation by staff skilled in neonatal care 2

Addressing the Constipation

The constipation (2-3 days without stool) is not a concerning finding in this context:

• It is not abnormal for infants to go several days without stooling [@clinical context from transcript@]
• The soft, non-tender abdomen with normal bowel sounds and comfortable infant makes pathologic constipation unlikely [@clinical context@]
• The "skid marks" represent normal stool remnants, not concerning findings [@clinical context@]

Critical Pitfalls to Avoid

• Never rely on clinical appearance alone - well-appearing infants can have bacteremia or meningitis 1
• Never use urine collection bags instead of catheterization 1
• Never delay lumbar puncture in this age group based on clinical criteria 1
• Never fail to obtain cultures before starting antibiotics as this compromises diagnostic accuracy 1
• Never discharge home without full evaluation in infants under 28 days with documented fever ≥38°C (100.4°F) 1, 2

Follow-Up Instructions

While the physician in the transcript provided home monitoring instructions, current guidelines mandate hospitalization for all febrile infants under 28 days 1. The threshold for concern (fever ≥101°F or 38.3°C with ill appearance) mentioned in the encounter is appropriate for older infants but not for this age group where any fever ≥38°C (100.4°F) requires full evaluation 2, 1.