Description

• Bacterial meningitis is an inflammation of the pia-arachnoid, its fluid and fluid of ventricles:
  • Always cerebrospinal
• System(s) affected: Nervous

• Bacterial meningitis is a medical, neurologic, and sometimes neurosurgical emergency. Streptococcuspneumoniae is the most common pathogen that causes bacterial meningitis in adults. Overall case fatality rate in adults with bacterial meningitis between 2003 and 2007 in the US was 16.4% (1).
• Signs and symptoms may be less evident and less specific in elderly and pediatric patients.

Epidemiology

• Predominant age: Neonates, infants, and elderly
• Predominant sex: Male = Female

Varies with age:

• <2 months: 80/100,000
• 2–23 months: 7/100,000
• 2–10 years: 0.5/100,000
• 11–17 years: 0.4/100,000
• 18–34 years: 0.66/100,000
• 35–49 years: 0.95/100,000
• ≥65 years: 1.92/100,000

Risk Factors

• Immunocompromising condition
• Alcoholism, diabetes, chronic conditions
• Neurosurgical procedure/head injury
• Abdominal surgery
• In neonates: Prematurity, low birth weight, premature rupture of membranes, maternal peripartum infection, and urinary tract abnormalities

Genetics
Individuals of Navajo Indian or American Eskimo descent may have genetic or acquired vulnerability to invasive disease.

General Prevention

• Prompt medical treatment for infections
• Strict aseptic techniques when treating patients with head wounds or skull fractures
• Look for CSF fistula with recurrent meningitis.
• Meningitis caused by Haemophilus influenzae has been nearly eliminated due to routine vaccination.
• Conjugate vaccines against S. pneumoniae may reduce the burden of disease in childhood and may produce herd immunity among adults and has resulted in significant declines in the incidence of pediatric bacterial meningitis.
• Persons with close contact to patients with meningococcal meningitis must receive chemoprophylaxis to eradicate carriage.

Pathophysiology

Bacterial infection causes inflammation of the pia-arachnoid and its fluid and the fluid of the ventricles.

Etiology

Bacteria are divided into age groups to guide empiric therapy (percentages indicate relative incidence of cases). Any organism can cause meningitis in any age group. Guide therapy by culture whenever possible:

• Neonates (<1 month):
  • Group B Streptococcus: 50%
  • Escherichia coli: 25%
  • Other gram-negative rods: 8%
  • Listeria monocytogenes: 6%
  • S. pneumoniae: 5%
  • Group A Streptococcus: 4%
  • H. influenzae: 3%
• Infants (≥1 month and <3 months):
  • Group B Streptococcus: 39%
  • Gram-negative bacilli: 32%
  • S. pneumonia: 14%
• In adults up to age 60 years:
  • S. pneumoniae: 60%
  • Neisseria meningitidis: 20%
  • H. influenzae: 10%
  • L. monocytogenes: 6%
  • Group B Streptococcus: 4%
• In adults age ≥60 years:
  • S. pneumoniae: 70%
  • L. monocytogenes: 20%
  • N. meningitidis: 3–4%
  • Group B Streptococcus: 3–4%
  • H. influenzae: 3–4%

Commonly Associated Conditions

The following conditions are associated with a worse prognosis:

• Coma
• Seizures
• Alcoholism
• Old age
• Infancy
• Diabetes mellitus
• Multiple myeloma
• Head trauma