Meningitis - Acute, Bacterial

Definition

Acute bacterial meningitis is a rapid-onset infection of the meninges, the protective membranes covering the brain and spinal cord, caused by bacterial pathogens and associated with significant morbidity and mortality if untreated.

Epidemiology

• Incidence highest in children <5 years and elderly adults.
• Global incidence: ~1–2 per 100,000 in high-income countries; higher in low- and middle-income countries.
• Outbreaks can occur in closed populations (dormitories, military camps).
• Mortality ranges from 5–25% depending on pathogen and age.
• Common pathogens vary by age: Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae type b.

Etiology

• Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae type b.
• Other bacteria: Listeria monocytogenes (neonates, elderly, immunocompromised).
• Post-neurosurgical meningitis or head trauma may involve Staphylococcus spp. or Gram-negative bacilli.
• Risk factors: immunodeficiency, complement deficiency, asplenia, chronic diseases, prior infection.

Pathophysiology

• Bacteria invade the bloodstream and cross the blood-brain barrier.
• Replication in CSF triggers intense inflammatory response.
• Neutrophil influx and release of cytokines cause meningeal edema and increased intracranial pressure.
• Cerebral blood flow and oxygen delivery are compromised, leading to neuronal injury.
• Complications include cerebral edema, hydrocephalus, vasculitis, and septic shock.