A 3-day-old term neonate born to a mother with prolonged rupture of membranes (>18 hours) presents with fever, poor feeding, and lethargy. Blood culture is sent. What is the most common causative organism of early-onset neonatal sepsis in this clinical scenario?

Explanation

## Most Common Cause of Early-Onset Neonatal Sepsis **Key Point:** Group B Streptococcus (GBS) is the most common cause of early-onset neonatal sepsis (EONS), accounting for approximately 40–50% of bacterial EONS cases in developed countries. ### Epidemiology of EONS Pathogens | Organism | Frequency | Timing | Risk Factors | |----------|-----------|--------|---------------| | **Group B Streptococcus** | 40–50% | 0–72 hours | Maternal colonization, prolonged ROM, prematurity | | E. coli (esp. K1) | 30–40% | 0–72 hours | Maternal GI colonization, prolonged ROM | | Listeria monocytogenes | 5–10% | 0–72 hours | Maternal listeriosis, immunocompromise | | S. aureus | <5% (EONS) | Late-onset (>72 hrs) | Nosocomial acquisition, skin flora | ### Pathogenesis of GBS Sepsis 1. **Maternal colonization** — GBS colonizes the maternal genital tract (vagina/rectum) in 10–30% of pregnant women. 2. **Vertical transmission** — Ascending infection or aspiration of colonized amniotic fluid during delivery. 3. **Neonatal invasion** — GBS crosses mucosal barriers and enters the bloodstream; crosses blood–brain barrier → meningitis (30% of EONS cases). **High-Yield:** Prolonged rupture of membranes (>18 hours) significantly increases the risk of vertical transmission of GBS and other maternal flora. ### Clinical Presentation of GBS EONS - Onset within first 72 hours of life (typically 6–48 hours). - Respiratory distress, fever/hypothermia, poor feeding, lethargy, irritability. - Septic shock, meningitis (30% of cases), or focal infection (osteomyelitis, arthritis). **Clinical Pearl:** GBS meningitis in neonates presents with subtle signs — irritability, poor feeding, seizures — and requires a high index of suspicion. Lumbar puncture is mandatory in all suspected EONS cases. **Mnemonic:** **GBSEONS** — Group B Strep is the #1 Early-Onset Neonatal Sepsis organism. ### Prevention & Management - **Intrapartum antibiotic prophylaxis (IAP):** Penicillin G or ampicillin given to GBS-colonized mothers during labor reduces EONS risk by ~70%. - **Empiric therapy for EONS:** Ampicillin + gentamicin (covers GBS, E. coli K1, Listeria). - Cephalosporins are NOT first-line because they do not reliably cover Listeria. [cite:Nelson Textbook of Pediatrics 21e Ch 101]