Neonatal Sepsis: Early vs Late Onset and Empiric Antibiotic Selection

Early-Onset Sepsis: Epidemiology and Risk Factors

Early-onset sepsis (EOS, within 72 hours of birth) occurs in 0.5-0.8 per 1,000 live-born term infants and 3-4 per 1,000 very low birth weight (VLBW) infants. Group B Streptococcus (GBS) and Escherichia coli account for approximately 70% of EOS cases in term infants, with E. coli now the predominant pathogen in preterm infants. Risk factors include inadequate intrapartum GBS prophylaxis, prolonged rupture of membranes (above 18 hours), chorioamnionitis, maternal fever, and gestational age below 37 weeks. The Kaiser Permanente EOS Sepsis Risk Calculator integrates gestational age, maternal temperature, GBS status, duration of membrane rupture, and intrapartum antibiotic administration to generate infant-specific sepsis probability, reducing empiric antibiotic exposure by 40-50% compared to the CDC categorical approach.

Late-Onset Sepsis: Pathogens and Presentation

Late-onset sepsis (LOS, after 72 hours) affects 10-25% of VLBW infants, with coagulase-negative staphylococci (CoNS, 48%), S. aureus (8%), Enterococcus species (5%), and gram-negative bacilli (18%, including Klebsiella, E. coli, Pseudomonas, and Serratia) as the predominant pathogens. Candida species account for 9-12% of LOS in extremely low birth weight infants (below 1,000g). Clinical presentation includes temperature instability, feeding intolerance, lethargy, apnea, tachycardia, and poor perfusion. A high index of suspicion is essential, as clinical signs overlap significantly with non-infectious conditions (NEC, PDA, IVH). Serial CRP measurements at 0 and 24 hours have a negative predictive value of 99% for culture-proven sepsis, supporting safe antibiotic discontinuation.

Empiric Antibiotic Selection

For EOS, ampicillin (50 mg/kg IV every 12 hours in first week, every 8 hours for meningitis dosing at 75-100 mg/kg) plus gentamicin (4-5 mg/kg IV every 24-48 hours based on gestational age) remains the standard regimen, providing coverage against GBS, E. coli (most strains), Listeria, and Enterococcus. For LOS, vancomycin (15 mg/kg IV every 8-12 hours, targeting trough 10-15 mcg/mL) plus gentamicin or a third-generation cephalosporin (cefepime 50 mg/kg IV every 8-12 hours if Pseudomonas concern) provides appropriate broad-spectrum coverage. An antifungal (fluconazole 12 mg/kg loading then 6 mg/kg daily, or micafungin 10 mg/kg daily) should be added empirically if risk factors for invasive candidiasis are present (prior broad-spectrum antibiotics, TPN, central line, ELBW).