Meningitis in Infants and Children

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Core Lesion: Meningitis is an acute, life-threatening inflammation of the leptomeninges (the tissues covering the brain and spinal cord).
• The Pathogen Shift: The etiology of this infection is heavily age-dependent. In neonates (<1 month), the immature immune system is highly vulnerable to Group B Streptococcus (the most common pathogen), Escherichia coli, and Listeria monocytogenes. Viral pathogens, notably Herpes Simplex Virus (HSV), can also cause severe, destructive meningoencephalitis.
• The Inflammatory Cascade: Unhindered bacterial proliferation in the cerebrospinal fluid (CSF) triggers a massive cytokine release. This inflammatory response breaks down the blood-brain barrier, causing cerebral edema, increased intracranial pressure (ICP), and decreased cerebral perfusion pressure. Untreated bacterial meningitis has a mortality rate of nearly 100%, and even with rapid intervention, survivors are at high risk for permanent neurologic sequelae.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization (ABCs): A child who does not respond to voice or has an impaired conscious level requires urgent airway securement. Administer supplemental oxygen to maintain SpO2 > 94%.
• The "Sixth Vital Sign": Check a bedside blood glucose (BMG) immediately in all sick children to rule out hypoglycemia as a cause of altered mental status.
• Hemodynamic Resuscitation: If there are signs of shock (tachycardia, capillary refill time > 2 seconds, mottled skin, purpuric rash, or depressed consciousness), immediately administer a fluid bolus of 0.9% saline 20 mL/kg IV/IO.
• First-Line Empiric Antimicrobials (Do Not Delay):
• If meningococcal disease is suspected: Administer parenteral benzylpenicillin or cefotaxime as soon as possible.
• Age < 3 months: You must add Ampicillin to the standard broad-spectrum regimen to specifically cover Listeria monocytogenes.
• Viral Coverage: Administer Acyclovir to any ill or febrile infant with a history of maternal HSV, skin vesicles, seizures, or focal neurologic signs.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Top "Can't-Miss" Mimics (AEIOU TIPS):
• Encephalitis: Often presents with focal neurologic deficits, movement disorders, or personality changes.
• Sepsis / Meningococcemia: Systemic shock with a rapidly spreading purpuric rash.
• Inborn Errors of Metabolism: Mimics neonatal sepsis; consider if profound hypoglycemia or hyperammonemia is present.
• Intracranial Hemorrhage / Non-Accidental Trauma: Suspect if the infant has altered mental status with no infectious prodrome.
• Prioritized Diagnostic Workup:
• Stat Labs: Bedside glucose, complete blood count (FBC), electrolytes (U&E), Ca2+, Mg2+, PO4, liver function tests, coagulation screen, and CRP.
• Cultures: Blood cultures must be drawn.
• Lumbar Puncture (LP): Gold standard for diagnosis. Send CSF for cell count, Gram stain, glucose, protein, bacterial culture, and a Biofire FilmArray meningitis/encephalitis PCR panel.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• Visual Skin Assessment: You must completely undress the child to actively look for petechial or purpuric rashes (indicative of meningococcemia) or vesicular rashes (indicative of HSV).
• Brain CT Scan Checklist: A head CT is not routinely required before an LP in a normal pediatric patient. However, the resident must obtain a brain CT scan before the LP if there is suspicion of increased Intracranial Pressure (ICP) or structural disease. Look for the following clinical red flags that mandate a CT:
• Confusion or coma.
• Cushing's triad (hypertension + bradycardia).
• Papilledema on fundoscopy.
• Focal neurological signs.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• Bacterial Meningitis Score (BMS): A highly tested, validated clinical decision rule used to stratify the risk of bacterial meningitis in children presenting with CSF pleocytosis. A patient is at high risk for bacterial meningitis if they meet any of the following criteria:
• Positive CSF Gram Stain
• CSF Absolute Neutrophil Count (ANC) (\ge 1000) cells/(\mu)L
• CSF Protein (\ge 80) mg/dL
• Peripheral ANC (\ge 10,000) cells/(\mu)L
• History of a seizure before or at presentation
• Clinical Disposition: If a child's presentation puts bacterial meningitis in the differential but it is not highly suspected, risk stratification tools can guide whether to withhold antibiotics pending CSF results. However, if the child is ill or meningitis is highly suspected, treat immediately and admit to the PICU.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• The LP Delay Trap: Withholding life-saving empiric antibiotics to successfully obtain a pristine cerebrospinal fluid sample or while waiting for a CT scan. Critical Action: Antibiotic and antiviral therapy for a patient with suspected bacterial meningitis should never be delayed by a lumbar puncture or neuroimaging.
• The Hypoglycemia Trap: Assuming a seizing or comatose child solely has a primary neurologic infection without checking metabolism. Critical Action: Treat hypoglycemia immediately; check bedside blood glucose in all sick children.
• The Listeria Omission: Forgetting that neonates and young infants have a unique microbiological profile. Critical Action: You must add Ampicillin to the regimen for any infant < 3 months old to cover Listeria.

7. MCQ MASTERCLASS (Written Exam Tips)

• The "Hypothermia" Buzzword: In board questions, while older children present with high fever and nuchal rigidity, neonates with bacterial meningitis frequently present with hypothermia instead. This is a classic distinguishing feature.
• The "21-Day-Old" Pathogen: If a vignette describes a 3-week-old with a bulging fontanelle and CSF pleocytosis, the most likely bacterial pathogen is Group B Streptococcus.
• The "CT vs. LP" Distractor: A classic question features a toxic child with altered mental status and focal neurologic signs. The options will include "Perform Lumbar Puncture." Always mark this incorrect. Focal signs or coma mandate a Head CT before LP due to the risk of herniation from increased ICP.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Resuscitation Hook: "I am presented with an ill-appearing, lethargic infant. I will immediately assess the Pediatric Assessment Triangle, secure the airway, place the patient on continuous monitors, and order a stat bedside glucose to rule out hypoglycemia. I will establish IV access and administer a 20 mL/kg normal saline bolus for any signs of shock."
• The Workup & Treatment Pivot: "Given the altered mental status and bulging fontanelle, I am highly concerned for bacterial meningitis or HSV encephalitis. I will order a full sepsis workup, including blood cultures. Most importantly, I will NOT delay antimicrobial therapy for imaging or a lumbar puncture. I am ordering IV Ceftriaxone, Vancomycin, IV Acyclovir, and, because the infant is under 3 months of age, IV Ampicillin to cover Listeria."
• The Diagnostic Articulation: "I will completely undress the child to examine for petechiae or vesicles. Because the patient is comatose—a sign of potentially increased ICP—I will defer the lumbar puncture, obtain a non-contrast Head CT, and consult the Pediatric Intensive Care Unit for immediate transfer."