Aetiology

The most probable causative organism is age dependent:

• neonates
  • can be
    • early - occurring during the first week of life, primary mode of infection is by vertical transmission (mother to child) through the birth canal
    • late - occurring between the second and sixth week, transmission is nosocomial or from person to person
  • causative agents include;
    • Streptococcus agalactiae (group B streptococcus)
    • E.coli and gram negatives
    • Streptococcus pneumoniae
    • Listeria monocytogenes
• children (beyond neonatal age)
  • Haemophilus influenzae type b
    • since the introduction of the vaccine H. influenza type b in 1990s, this pathogen is no longer a major cause of bacterial meningitis n children
  • Neisseria meningitidis – Meningococcus
    • most N. meningitidis colonisations are asymptomatic, but occasionally the organism invades the bloodstream (usually within a few days of a susceptible person acquiring the organism) to cause meningococcal disease which includes
      • bacterial meningitis (15% of cases)
      • septicaemia (25% of cases)
      • a combination of the two syndromes (60% of cases)
    • tuberculosis
  • Streptococcus pneumoniae - Pneumococcus
• adults
  • Streptococcus pneumoniae – Pneumococcus
  • Neisseria meningitidis – Meningococcus
    • mostly seen in adolescents and mostly caused by serogroup B
    • incidence has declined in the past decade
  • Listeria monocytogenes
    • commonly associated with old age and immunocompromised state
  • Haemophilus influenza
  • Staphylococcus aureus
• immunocompromised patients
  • Pneumococcus
    • predisposing conditions include: splenectomy or hyposplenic state, chronic kidney or liver disease, HIV, alcoholism, diabetes
  • Haemophilus influenza
    • seen in: diabetes, alcoholism, splenectomy or asplenic state, multiple myeloma
  • Listeria monocytogenes
    • associated with elderly patients (>60 years), in acquired immunodeficiencies (diabetes, cancer), use of immunosuppressive drugs
      

Reference:

• (1) van de Beek D et al. ESCMID guideline: diagnosis and treatment of acute bacterial meningitis. Clin Microbiol Infect. 2016;22 Suppl 3:S37-62.
• (2) NICE (June 2010). Meningitis (bacterial) and meningococcal septicaemia in under 16s: recognition, diagnosis and management. Available at https://www.nice.org.uk/guidance/cg102 (Accessed on June 2023)