Background

The epidemiology of acute bacterial meningitis has changed drastically since the introduction of routine vaccination with the Haemophilus influenzae type B (Hib) in and the polyvalent conjugated pneumococcal vaccine.¹ The incidence of invasive Hib infection among young children (<5 years of age) has decreased by 99%, from 46 to 100 cases per 100,000 children to <1 case per 100,000 children.² Hib vaccination is a 3 to 4 immunization series that occurs at 2, 4, possibly 6 (depending on the type of vaccine used), and a booster at 12 to 15 months.³ Similarly, the current 13‐valent pneumococcal conjugated vaccine is administered at 2, 4, 6, and 12 to 15 months. When the 7‐valent pneumococcal vaccination was introduced in 2000, the rate of pneumococcal meningitis decreased by 66% from 7.7 per 100,000 to 2.6 per 100,000 in children less than 2 years of age. A decline of 51.5% was seen in older children 2 to 4 years of age.⁴ Meningococcal disease has two peaks of increased incidence, the highest is still in young children less than 4 years at 0.69 per 100,000 persons, and then in the teenage years, 15 to 19 years, at 0.29 per 100,000 persons.⁵ Currently, there is a two‐dose schedule of the meningococcal vaccine that is to be given at 11 to 12 years and then a booster at 16 years.³

Vaccination has created four distinct populations of children at different risks of acute bacterial meningitis: neonates less than <1 month, infants 1–2 months, unvaccinated or under‐vaccinated children, and vaccinated children. However, small areas of unimmunized and under‐immunized children remain and may continue to serve as potential reservoirs for disease. Despite vaccination, there will always be a child with an underlying immunodeficiency or infection from a strain not covered in current vaccines.

Preterm and infants less than 28 days of age are at the highest risk for bacterial meningitis at 0.25 to 0.32 per 1000 live births.⁶ This is likely due to their immature immune system and intrapartum bacterial exposures. Group B Streptococcus (GBS) continues to be a leading pathogen in neonates despite widespread intrapartum surveillance and treatment, accounting for 40% of disease.⁷ Late‐onset (6 to 90 days) and very late onset (>90 days) GBS diseases have the highest rates and mortality in preterm neonates.⁸ Most mothers carried GBS in the rectovaginal flora and 6% of mothers had mastitis at the time of the late‐onset GBS diagnosis. Intrapartum antibiotics have been associated with delayed presentation of symptoms and milder GBS disease.⁸ Next to GBS, E. coli and other Gram‐negative bacteria have emerged as the second leading pathogen, attributing to 30% of meningitis infections. Listeria continues to be a lingering pathogen that still is considered in this age group (Table 23.1).