Emergency Medicine · Year 3 · from Emergency Medicine

Case 2: Febrile Infant - The 28-Day-Old with Fever

Patient Demographics

  • Age: 28 days
  • Sex: Male
  • Accompanied by: Both parents

Chief Complaint

"He feels warm and isn't acting right."

History of Present Illness

Parents bring their 28-day-old son for evaluation of fever. Temperature at home was 38.4C (101.1F) rectal. Infant has been less interested in feeding today, taking only 50% of usual volumes. Parents note he seems "fussy" and not easily consoled like usual. No cough, congestion, or diarrhea. No sick contacts. Parents are first-time parents and appropriately concerned.

Initial Assessment

Pediatric Assessment Triangle:

  • Appearance: Irritable when examined, settles briefly with mother
  • Work of Breathing: Normal respiratory effort
  • Circulation: Pink, well-perfused

ESI Level: 2 - Febrile neonate requires immediate evaluation

Vital Signs:

  • Heart rate: 172 bpm
  • Respiratory rate: 42 breaths/min
  • SpO2: 98% on room air
  • Temperature: 38.6C (101.5F) rectal
  • Weight: 4.2 kg

Critical Concept: The Febrile Neonate (<28 days)

Why the concern?

  • Immature immune system
  • Risk of serious bacterial infection (SBI): 10-15%
  • Includes: UTI, bacteremia, meningitis
  • Pathogens: Group B Strep, E. coli, Listeria, HSV

This baby is 28 days old - at the upper limit of "neonate" but still HIGH RISK

Primary Survey

Airway: Patent, crying Breathing: Normal rate and effort Circulation: Well-perfused, strong pulses Disability: Irritable but consolable, normal tone, normal fontanelle Exposure: No rashes, no petechiae

Secondary Survey

SAMPLE History:

  • Symptoms: Fever, irritability, decreased feeding
  • Allergies: None
  • Medications: Vitamin D drops
  • PMH: Full-term (39 weeks), uncomplicated SVD, no NICU stay
  • Last Meal: 3 hours ago, took 45mL (usually 90mL)
  • Events: Fever noted 4 hours ago

Birth History:

  • GBS status: Negative
  • ROM: 8 hours before delivery
  • Maternal fever: None
  • Apgars: 8, 9

Detailed Physical Exam:

General: Intermittently irritable, settles with consoling HEENT:

  • Fontanelle soft, flat
  • TMs normal
  • No conjunctivitis
  • Mucous membranes moist

Neck: Supple, no meningismus (difficult to assess in neonates)

Cardiovascular:

  • Tachycardic (appropriate with fever)
  • No murmur
  • Strong pulses, cap refill 2 seconds

Respiratory:

  • Clear breath sounds
  • No distress

Abdomen:

  • Soft, non-distended
  • No masses
  • Normal umbilicus (no erythema, discharge)

GU:

  • Uncircumcised male
  • No scrotal swelling

Skin:

  • No rashes
  • No vesicles (HSV concern)
  • No petechiae

Neurological:

  • Normal tone
  • Symmetric movements
  • Strong suck reflex

Diagnostic Workup - Febrile Neonate Protocol

Required Studies:

  1. CBC with differential: WBC 18,400 with 68% neutrophils, 4% bands
  2. Blood culture: Obtained before antibiotics
  3. Urinalysis and urine culture: Catheterized specimen - UA positive (>10 WBC/hpf, positive LE)
  4. Lumbar puncture:
  • CSF WBC: 4 cells/μL (normal <20)
  • CSF protein: 85 mg/dL (normal for age)
  • CSF glucose: 48 mg/dL (serum 72) - ratio normal
  • Gram stain: No organisms
  • CSF culture: Sent
  • HSV PCR: Sent
  1. Metabolic panel: BMP normal
  2. Inflammatory markers: Procalcitonin 0.8 ng/mL

Diagnosis

Urinary tract infection in febrile neonate

  • High risk for bacteremia/urosepsis
  • Most common source of SBI in febrile infants

Management

Empiric Antibiotics (given before culture results):

  • Ampicillin 50 mg/kg IV q8h (Listeria coverage)
  • Cefotaxime 50 mg/kg IV q8h (broad GN coverage, good CSF penetration)
  • Acyclovir 20 mg/kg IV q8h (HSV coverage - given any febrile neonate with irritability)

Note: Acyclovir started empirically given irritability; will discontinue if HSV PCR negative and clinically improving

Supportive Care:

  • IV fluids
  • Antipyretics (acetaminophen 15 mg/kg PR)
  • Continuous monitoring

Culture Results (48 hours)

  • Blood culture: Negative
  • Urine culture: E. coli >100,000 CFU/mL (confirms UTI)
  • CSF culture: Negative
  • HSV PCR: Negative

Antibiotic Adjustment

  • Discontinue ampicillin (no Listeria)
  • Discontinue acyclovir (HSV negative)
  • Continue cefotaxime, transition to ceftriaxone
  • Total IV antibiotic course: 7 days (given age)

Disposition

  • NICU/Pediatric floor admission
  • Complete IV antibiotic course
  • Renal ultrasound: Normal (no structural abnormality)
  • Voiding cystourethrogram: Deferred to outpatient (will need given age and UTI)
  • Discharged day 7, follow-up with pediatrics and urology

Teaching Points

  1. Fever in neonate = sepsis workup: Full evaluation including LP mandatory in <28 days
  2. Don't miss HSV: Acyclovir empirically if irritability, seizures, vesicles, or CSF pleocytosis
  3. UTI most common SBI: Catheterized specimen required; bag specimens unacceptable
  4. Blood culture before antibiotics: But don't delay antibiotics for LP if patient unstable
  5. Ampicillin + cefotaxime (or gentamicin): Standard empiric regimen for neonatal sepsis
  6. Ceftriaxone avoided in neonates: Risk of bilirubin displacement; use cefotaxime instead
  7. Follow-up imaging: UTI in young infant requires renal US; VCUG to evaluate for vesicoureteral reflux

Clinical Image

Image Description: Illustration demonstrating proper positioning for lumbar puncture in an infant, with the baby held in lateral decubitus position with hips and knees flexed, spine curved, while an assistant stabilizes the patient and monitors for respiratory compromise.

Attribution: Image from Wikimedia Commons, Infant lumbar puncture positioning. Public domain. Source: https://commons.wikimedia.org/wiki/File:Lumbar_puncture_infant.jpg

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