aetiology

Last edited 06/2018 and last reviewed 06/2021

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, chornic 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) National Institute for Health and Clinical Excellence (NICE) 2017. Bacterial meningitis and meningococcal septicaemia in children