A 5-day-old preterm neonate (32 weeks gestation) admitted to the NICU develops signs of sepsis. Blood and cerebrospinal fluid cultures are obtained. The neonate has been on broad-spectrum antibiotics for 3 days without clinical improvement. Which is the most common causative organism of late-onset neonatal sepsis (LONS) in this NICU setting?

Explanation

## Most Common Cause of Late-Onset Neonatal Sepsis **Key Point:** Coagulase-negative Staphylococcus (CoNS), particularly *Staphylococcus epidermidis*, is the most common cause of late-onset neonatal sepsis (LONS), accounting for 30–50% of LONS cases in NICU settings. ### Epidemiology of LONS Pathogens | Organism | Frequency | Timing | Source | Risk Factors | |----------|-----------|--------|--------|---------------| | **CoNS** | 30–50% | >72 hours | Skin flora, indwelling catheters | Central lines, prolonged hospitalization | | Gram-negative rods (Klebsiella, E. coli, Pseudomonas) | 20–30% | >72 hours | Environmental, healthcare-associated | Prolonged antibiotic exposure, ventilation | | Staphylococcus aureus | 10–15% | >72 hours | Skin, healthcare-associated | Central lines, skin colonization | | Candida spp. | 5–10% | >72 hours (often >2 weeks) | Endogenous, environmental | Prolonged antibiotics, central lines, prematurity | ### Pathogenesis of CoNS LONS 1. **Source:** Skin commensal; colonizes indwelling central venous catheters, peripheral lines, or endotracheal tubes. 2. **Biofilm formation:** CoNS produces slime/polysaccharide capsule → adherence to foreign bodies and resistance to antibiotics. 3. **Translocation:** Breach of skin barrier (line insertion, prolonged hospitalization) allows entry into bloodstream. 4. **Timing:** Typically develops >72 hours after birth, often after 1–2 weeks of NICU stay. **High-Yield:** CoNS is a **nosocomial pathogen** — acquisition occurs in the hospital environment, not from maternal flora. Prolonged central venous catheterization is the single greatest risk factor. ### Clinical Presentation of CoNS LONS - Fever, lethargy, poor feeding, abdominal distension, thrombocytopenia. - Often presents as **catheter-related bloodstream infection (CRBSI)**. - Meningitis is less common than with GBS or E. coli. - May have a more indolent course compared to early-onset sepsis. **Clinical Pearl:** CoNS bacteremia in a neonate with a central line should raise suspicion for CRBSI. Line removal (if possible) combined with appropriate antibiotics is often necessary for cure. ### Distinction: EONS vs. LONS ```mermaid flowchart TD A[Neonatal Sepsis]:::outcome --> B{Age at Onset}:::decision B -->|0–72 hours| C[Early-Onset Sepsis]:::outcome B -->|>72 hours| D[Late-Onset Sepsis]:::outcome C --> E[Vertical transmission from mother]:::action C --> F[GBS, E. coli K1, Listeria]:::outcome D --> G[Nosocomial acquisition in NICU]:::action D --> H[CoNS, Gram-negative rods, S. aureus, Candida]:::outcome ``` ### Management of CoNS LONS - **Empiric therapy:** Vancomycin + third-generation cephalosporin or aminoglycoside (covers CoNS and gram-negative rods). - **Line management:** Remove central line if possible; blood cultures from line and peripheral site to confirm CRBSI. - **Antibiotic duration:** 7–10 days for bacteremia; longer if meningitis or endocarditis. - **Susceptibility testing:** CoNS may be methicillin-resistant (MRSE) — vancomycin is preferred. **Mnemonic:** **LONS-CoNS** — Late-Onset Neonatal Sepsis = Coagulase-Negative Staphylococcus (most common). [cite:Nelson Textbook of Pediatrics 21e Ch 101]