Description

Bacterial infection of the meninges resulting in inflammation, pain, and systemic illness

Epidemiology

Predominant age: neonates, infants, and elderly; predominant sex: male = female

Incidence
Varies by age and pathogen

• 18 to 34 years: 0.66/100,000. 35 to 49 years: 0.95/100,000. 50 to 64 years: 1.73/100,000. ≥65 years: 1.92/100,000
• Group B Streptococcus: 0.25/100,000. Neisseria meningitidis: 0.19/100,00
• Haemophilus influenzae type B: 0.08/100,000. Listeria monocytogenes: 0.05/100,000

Prevalence
15,000 to 25,000 cases occur annually in United States.

Etiology and Pathophysiology

Community-acquired bacterial meningitis is most commonly due to Streptococcus pneumoniae (50%) and N. meningitidis (30%). Nosocomial or postsurgical meningitis occurs after manipulation of the central nervous system (CNS) space allowing for entry of pathogens. Newborns (<2 months): Group B Streptococcus, Escherichia coli, L. monocytogenes. Infants and children: S. pneumoniae, N. meningitidis, H. influenzae. Adolescents and young adults: N. meningitidis, S. pneumoniae. Immunocompromised adults: S. pneumoniae, L. monocytogenes, gram-negative bacilli such as Pseudomonas aeruginosa. Mixed bacterial infection in <1% of cases. Older adults: S. pneumoniae 50%, N. meningitidis 30%, L. monocytogenes 5%. 10% gram-negatives bacilli: E. coli, Klebsiella, Enterobacter, P. aeruginosa

Genetics
Some Native American populations appear to have genetic or acquired susceptibility to invasive disease.

Risk Factors

• Household or close contacts of case patients. Immunocompromised, alcoholism, diabetes, chronic disease. Neurosurgical procedure/head injury, close living quarters. Neonates: prematurity, low birth weight, premature rupture of membranes, maternal peripartum infection, and urinary tract abnormalities. Abnormal communication between nasopharynx and subarachnoid space (congenital, trauma), dural fistula. Parameningeal source: otitis, sinusitis, mastoiditis; trauma: skull fracture. Adults age >65 years, immunocompromised patients, and pregnant women are at risk for listeriosis; complement component deficiencies C3, C5 to C9, properdin, factor H, and factor D
• HIV infection. Functional or anatomic asplenia. Patients taking eculizumab and ravulizumab are at increased risk for meningococcal disease; microbiologists who are routinely exposed to isolates of N. meningitidis
• Military recruits, young college students living in crowded residence halls

General Prevention

• Consider CSF fistula in cases of recurrent meningitis; aseptic techniques for head wounds or skull fractures
• Meningitis caused by H. influenzae type B has decreased 55% with routine vaccination. Conjugate vaccines against S. pneumoniae may reduce the burden of disease in childhood; chemoprophylaxis for close contacts of meningococcal meningitis patients

Commonly Associated Conditions

Factors associated with a worse prognosis: alcoholism, old age, infancy, diabetes mellitus, multiple myeloma, head trauma, seizures, immunocompromised, coma, sepsis, sinusitis