Pediatric Fever in the Young Infant (0–90 Days)
Evidence-based emergency risk stratification and protocolized management of febrile young infants aged 0 to 90 days: bacteremia, bacterial meningitis, and urinary tract infections caused by Group B Streptococcus (GBS), E. coli, and Listeria monocytogenes; neonatal herpes simplex virus (HSV-1 and HSV-2) vesicles and encephalitis; application of validated decision rules (Rochester, Boston, Philadelphia, and modern PECARN/AAP guidelines); lumbar puncture indications; and empiric IV antibiotic/acyclovir regimens.
Resuscitation Quick Actions • First 2 Minutes
Rectal Temperature Mandate
Rectal temp >= 38.0°C (100.4°F); axillary and tympanic readings are unreliable; a reported home rectal fever counts as a true fever
0–28 Days Full Workup
CBC, Blood Culture, Catheter Urinalysis + Culture, Lumbar Puncture (CSF cell count, protein, glucose, culture, enterovirus/HSV PCR)
0–28 Days Empiric Meds
Ampicillin 50 mg/kg IV q8h (covers Listeria & Enterococcus) + Ceftazidime 50 mg/kg IV q8h (or Gentamicin 2.5 mg/kg IV q8h)
Acyclovir Indications
Add Acyclovir 20 mg/kg IV q8h if: maternal history of HSV, vesicles, seizures, CSF pleocytosis, hypothermia, or transaminitis
Avoid Ceftriaxone in Neonates
DO NOT use Ceftriaxone in infants < 28 days (displaces bilirubin from albumin causing kernicterus; precipitates with IV calcium)
29–60 Days Low-Risk Biomarkers
Procalcitonin <= 0.5 ng/mL, CRP <= 20 mg/L, ANC <= 4000/mcL, and negative catheter UA -> Safe to defer LP and observe
Bottom-Line Clinical Pearl
Any infant <= 28 days with a rectal temperature >= 38.0°C (100.4°F) requires a full sepsis evaluation (blood culture, catheterized urinalysis/culture, and lumbar puncture) and immediate admission on IV Ampicillin + Ceftazidime/Gentamicin +/- Acyclovir. In infants aged 29–60 days, modern PECARN and AAP guidelines allow risk-stratification using inflammatory biomarkers (procalcitonin <= 0.5 ng/mL, CRP <= 20 mg/L, absolute neutrophil count <= 4,000) and clean catheter urinalysis to safely defer lumbar puncture and avoid hospital admission in low-risk patients. Never treat an ear thermometer reading as accurate; rectal temperature is the mandatory gold standard.
Young infants have immature humoral and cell-mediated immunity, impaired neutrophil chemotaxis, deficient complement levels, and permeable blood-brain barriers, placing them at profound risk for invasive bacterial infections (IBIs): bacteremia, urinary tract infection (UTI), and bacterial meningitis. Physical examination is notoriously unreliable in neonates, who can present with subtle lethargy, poor feeding, or tachypnea without focal signs.
| Infant Age Tier | Primary Pathogens | Clinical Workup Algorithm | Empiric Antimicrobial Regimen |
|---|---|---|---|
| 0 to 28 Days (Neonatal) | Group B Streptococcus (GBS), Escherichia coli, Listeria monocytogenes, Klebsiella, Herpes Simplex Virus (HSV-1/2) | Mandatory Full Sepsis Workup: Blood culture, catheterized UA/culture, Lumbar Puncture (CSF analysis & viral PCR). Inpatient admission mandatory. | Ampicillin (50 mg/kg IV q8h) + Ceftazidime (50 mg/kg IV q8h) OR Gentamicin (2.5 mg/kg IV q8h). Add Acyclovir (20 mg/kg IV q8h) if HSV risk factors present. |
| 29 to 60 Days | Escherichia coli, Group B Streptococcus, Streptococcus pneumoniae, Neisseria meningitidis | Risk-Stratified Workup: Catheter UA, blood culture, and inflammatory biomarkers (Procalcitonin, CRP, ANC). Lumbar puncture indicated if biomarkers abnormal or ill-appearing. | If abnormal biomarkers or ill: Ceftriaxone (50 mg/kg IV; note: safe once > 28 days) +/- Ampicillin. If all biomarkers low-risk: can defer LP and manage outpatient with 24h follow-up. |
| 61 to 90 Days | Escherichia coli (UTI is #1), Streptococcus pneumoniae, Enterovirus | Targeted Workup: Catheterized urinalysis and culture. Blood culture/CBC only if unvaccinated or clinically unwell. | Antipyretics; oral antibiotics if UTI identified; outpatient discharge if well-appearing and vaccinated. |
Critical Pitfall / Contraindication
CEFTRIAXONE CONTRAINDICATION IN NEONATES (< 28 DAYS): Ceftriaxone is strictly contraindicated in neonates under 28 days of age. It competitively binds albumin and displaces bilirubin, causing free hyperbilirubinemia and kernicterus (bilirubin encephalopathy). Furthermore, when co-infused with calcium-containing solutions (e.g., parenteral nutrition, Ringer's), it forms insoluble calcium-ceftriaxone crystalline precipitates in the lungs and kidneys. Use Ceftazidime or Gentamicin instead.
Test Your Pediatric Fever in the Young Infant (0–90 Days) Clinical Acumen
Directly launch an active-recall practice block from our 8,400+ validated COMLEX Level 1, 2-CE & 3 board question bank with complete explanations.
Related Emergency Protocols & Differentials
Pediatric Bacterial Meningitis & Sepsis
Septic shock and critical meningitis algorithms.
Open Protocol Related EM ProtocolBrief Resolved Unexplained Events (BRUE)
Risk stratification in young infants.
Open Protocol Related EM ProtocolAltered Mental Status & Coma
Evaluation of pediatric encephalopathy.
Open Protocol