## Early-Onset Neonatal Sepsis (EOS) — Microbiology **Key Point:** Group B Streptococcus (GBS) is the leading cause of EOS in term and near-term infants, accounting for approximately 40–50% of bacterial EOS cases. ### Epidemiology of EOS Pathogens | Organism | Frequency in EOS | Risk Factor | Maternal Source | | --- | --- | --- | --- | | **GBS (Streptococcus agalactiae)** | 40–50% | Vaginal colonization | Vertical transmission during delivery | | **E. coli (esp. K1 capsule)** | 30–40% | Prematurity, prolonged rupture of membranes | Vaginal flora | | **Listeria monocytogenes** | 5–10% | Maternal listeriosis, immunosuppression | Transplacental or intrapartum | | **Coagulase-negative Staph** | <5% in EOS | Prematurity, invasive procedures | Skin flora (late-onset) | **High-Yield:** GBS colonizes the maternal genital tract in 15–40% of pregnant women. Vertical transmission during vaginal delivery is the primary route of neonatal infection. Intrapartum antibiotic prophylaxis (IAP) with penicillin or ampicillin significantly reduces GBS transmission. ### Clinical Pearl EOS typically presents within the first 72 hours of life (often within 24 hours). GBS causes both sepsis and meningitis; meningitis occurs in ~10% of GBS-infected neonates. ### Mnemonic: EOS Pathogens — "GEL" - **G** = Group B Streptococcus (most common) - **E** = E. coli (especially K1) - **L** = Listeria monocytogenes These three account for >90% of bacterial EOS in term infants.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.