Neonatal meningitis

Etiology & Pathogenesis - The Tiny Invaders

• Causative Agents:

  • Early Onset (< 7 days): 📌 GEL
    • Group B Strep (GBS) - Most common
    • E. coli (esp. K1 strain)
    • Listeria monocytogenes
  • Late Onset (≥ 7 days):
    • GBS, E. coli
    • Staphylococci, Pseudomonas (nosocomial)

• Pathogenesis:

  • Source: Maternal GU tract (early) or environment (late).
  • Route: Hematogenous spread → bacteremia → meningeal seeding.

⭐ E. coli with the K1 capsular antigen is highly neuroinvasive, making it a leading cause of gram-negative neonatal meningitis.

Clinical Features - Subtle Signs, Big Trouble

Signs are notoriously non-specific and subtle in neonates. Look for a constellation of findings rather than a single sign.

• Systemic: Temperature instability (fever or hypothermia), lethargy, poor feeding, irritability, vomiting, respiratory distress.
• Neurologic: Seizures (often subtle: e.g., staring, lip-smacking), altered sensorium, high-pitched cry, apnea.
• Fontanelle: Bulging or full anterior fontanelle is a late and unreliable sign.
• Classic Signs: Nuchal rigidity and Kernig's/Brudzinski's signs are typically absent.

⭐ Paradoxical irritability (crying when cuddled, quiet when left alone) is a subtle but important clue.

Diagnosis - The Spinal Tap Story

• Lumbar Puncture (LP) is mandatory on suspicion of meningitis.
  • Contraindications: Cardiorespiratory instability, signs of ↑ Intracranial Pressure (ICP) like bulging fontanelle or focal deficits, infection at the puncture site, significant coagulopathy.
• CSF Analysis - Key Findings (Bacterial):
  • Appearance: Turbid/Purulent
  • Cells: ↑↑ Neutrophils (>80%); Total count often >1000/mm³
  • Protein: ↑ >100-150 mg/dL
  • Glucose: ↓ <40 mg/dL or CSF/Blood glucose ratio <0.4
  • Gram Stain & Culture: Gold standard for pathogen identification.
• Adjunctive Tests:
  • Blood Culture: Often positive.
  • Latex Agglutination Test (LAT): For GBS, S. pneumoniae antigens.

⭐ In a traumatic (bloody) tap, a corrected WBC count is crucial. A common rule is to subtract 1 WBC for every 500-1000 RBCs in the CSF to estimate the true level of pleocytosis.

Management - Bug-Busting Bootcamp

• Empiric Antibiotics: Initiate ASAP after lumbar puncture.

• Duration of Therapy (Minimum):

  • Group B Strep: 14 days
  • Listeria monocytogenes: 14-21 days
  • Gram-Negative Bacilli (e.g., E. coli): 21 days

• Supportive Care:

  • Maintain fluid & electrolyte balance
  • Control seizures (Phenobarbital)
  • Monitor for complications (SIADH, hydrocephalus)

⭐ Exam Pearl: Cefotaxime is preferred over Ceftriaxone in neonates. Ceftriaxone displaces bilirubin from albumin, increasing the risk of kernicterus, and can cause biliary sludging.

Complications & Prognosis - The Aftermath

• Acute: SIADH, subdural effusion/empyema, ventriculitis, brain abscess, communicating hydrocephalus.
• Long-term Sequelae (25-50%):
  • Sensorineural hearing loss (most common)
  • Intellectual disability, epilepsy
  • Cerebral palsy, visual impairment
• Prognosis:
  • Mortality: 10-15% (GBS/E. coli), higher with other gram-negatives.
  • Worse with seizures, coma, high CSF protein.

⭐ Sensorineural hearing loss is the most common sequela. All survivors require an auditory assessment (BERA/OAE) before discharge.

High‑Yield Points - ⚡ Biggest Takeaways

• Group B Streptococcus (GBS) is the leading cause of early-onset meningitis, while Coagulase-Negative Staphylococci (CoNS) is common in late-onset cases.
• Clinical signs are often non-specific (lethargy, poor feeding). A bulging fontanelle is a more specific and crucial sign.
• Lumbar puncture is the cornerstone of diagnosis; definitive diagnosis is by CSF culture.
• Empirical treatment is typically Ampicillin + Gentamicin or Ampicillin + Cefotaxime.
• Carries a high risk of severe long-term neurological sequelae.