A 5-day-old neonate born to a mother with intrapartum fever and positive GBS colonization develops sepsis. Which finding best distinguishes Group B Streptococcal (GBS) sepsis from *Escherichia coli* K1 sepsis in early-onset neonatal sepsis?

Explanation

## GBS vs *E. coli* K1 Sepsis: Key Discriminators ### Clinical Presentation Comparison | Feature | GBS Sepsis | *E. coli* K1 Sepsis | | --- | --- | --- | | **Meningitis rate** | 5–10% in bacteremia, rare in early EONS | 40–80% in bacteremia, very common in EONS | | **CNS involvement** | Uncommon in EONS (more in LONS) | Highly prevalent; K1 capsule evades immune system | | **Presentation** | Respiratory distress, septic shock | Sepsis ± meningitis (often concurrent) | | **Mortality** | 4–6% with treatment | 5–15% even with treatment; higher if meningitis | | **CSF findings** | Sterile in most EONS cases | Positive culture in ~50% of bacteremic cases | **Key Point:** *E. coli* K1 has a marked tropism for the meninges due to its K1 polysaccharide capsule, which mimics neural tissue and evades complement-mediated killing. GBS, by contrast, rarely causes meningitis in early-onset disease (meningitis is more common in LONS GBS). **High-Yield:** The CNS involvement rate is the single best clinical discriminator — *E. coli* K1 meningitis occurs in 40–80% of bacteremic cases, whereas GBS meningitis is uncommon in EONS (< 10%). **Clinical Pearl:** Any neonate with EONS and positive blood culture for Gram-negative rod should be assumed to have meningitis until CSF culture is negative. Lumbar puncture is mandatory in *E. coli* K1 sepsis; it may be deferred in uncomplicated GBS sepsis if clinical response is good. **Mnemonic:** **E. coli K1 = Meningitis in Neonates (K1 capsule = CNS tropism)** [cite:Harrison Principles of Internal Medicine 21e Ch 141; Nelson Textbook of Pediatrics 21e Ch 102]