Question
A two-year-old child was brought to casualty with high grade fever, vomiting and drowsiness. On examination, the child had neck rigidity and other signs of meningeal irritation. CSF examination was suggestive of acute bacterial meningitis
- (a) List the bacteria causing acute bacterial meningitis 3 mark(s)
- (b) Describe the pathogenesis of pneumococcal meningitis 2 mark(s)
- (c) Describe the laboratory diagnosis of pneumococcal meningitis 3 mark(s)
- (d) Discuss the prevention of pneumococcal meningitis 2 mark(s)
Answer
a) Bacteria causing acute bacterial meningitis (varies by age): Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b are the classical agents in children beyond the neonatal period; Escherichia coli, Group B Streptococcus, and Listeria monocytogenes are more typical in neonates.
b) Pathogenesis of pneumococcal meningitis Streptococcus pneumoniae first colonizes the nasopharynx; from there it can invade the bloodstream (bacteraemia), often following an antecedent viral upper respiratory infection that damages mucosal defences. The organism’s polysaccharide capsule is antiphagocytic, allowing it to survive and multiply in the blood. It then crosses the blood-brain/blood-CSF barrier (choroid plexus) to seed the meninges. Once in the CSF — a compartment relatively deficient in complement and antibody — the organism multiplies unchecked; bacterial cell wall components (peptidoglycan, teichoic acid) trigger a marked host inflammatory response (release of TNF-α, IL-1, IL-6 by activated microglia/astrocytes), which drives increased blood-brain barrier permeability, cerebral oedema, raised intracranial pressure, and neuronal injury — the host inflammatory response, not just direct bacterial invasion, is a major contributor to the clinical severity and neurological sequelae.
c) Laboratory diagnosis
- CSF examination: turbid/cloudy appearance, neutrophilic pleocytosis, raised protein, and markedly reduced glucose.
- Gram stain of CSF — Gram-positive, lancet-shaped diplococci.
- CSF culture — on blood agar/chocolate agar; alpha-haemolytic, optochin-sensitive, bile-soluble colonies confirm S. pneumoniae.
- Latex agglutination test — rapid detection of pneumococcal capsular antigen directly in CSF, useful if antibiotics have already been given.
- Blood culture — often positive concurrently.
- PCR — rapid, sensitive detection.
d) Prevention Pneumococcal conjugate vaccine (PCV) — part of the routine infant immunization schedule, covering the major invasive serotypes; pneumococcal polysaccharide vaccine (PPSV23) for older children/adults and high-risk groups; prompt treatment of upper respiratory infections; and, since asplenic/hyposplenic individuals are at particular risk of overwhelming pneumococcal infection, vaccination is especially emphasized in this group.