Condition

Bacterial Meningitis in Adults

Editors: Yijia Li MD; Zbigniew Fedorowicz PhD, MSc, DPH, BDS, LDSRCS; Paritosh Prasad MD

American College of PhysiciansProduced in collaboration with American College of Physicians
Next Section >

Background Information

Description

  • Bacterial meningitis is a potentially life-threatening medical, neurologic, and sometimes neurosurgical emergency due to bacterial infection and inflammation of meninges.
    1
    ,
    2
    ,
    4
    • Community-acquired bacterial meningitis is caused by invasion of the central nervous system (CNS) by bacteria in the setting of bacteremia or by direct extension though dural defects or local infection.
    • Nosocomial or postsurgical bacterial meningitis occurs after manipulation of the CNS space allowing for entry of pathogenic organisms.

Epidemiology

Incidence/Prevalence

  • Introduction of the conjugate vaccine programs has resulted in large reductions in incidence of bacterial meningitis over the past few decades.
    2
    ,
    4
  • Globally, incidence of bacterial meningitis is reported to range from an estimated 0.9 cases per 100,000 population annually in high-income countries to an estimated 10-80 cases per 100,000 population annually in low-to-middle-income countries.
    1
    • The "meningitis belt" refers to a region that spans sub-Saharan Africa from Senegal and Gambia to Kenya and Ethiopia that experiences cyclic meningococcal meningitis epidemics. With the introduction of MenA vaccines to the region in 2010, epidemics caused by Neisseria meningitidis serogroup A have been eliminated in vaccinated areas of the meningitis belt (East Afr J Public Health 2010 Mar;7(1):20, CDC 2024 Feb).
  • United States:
    • About 13% of all meningitis and encephalitis cases in adults are bacterial meningitis.
      1
    • 15,000-25,000 cases occur in the United States annually.
      4
    • Following childhood vaccinations, bacterial meningitis has shifted from the pediatric to the adult population in United States. Median age of affected patients increased from 30.3 years in 1998-1999 to 41.9 years in 2006-2007 in the United States, based on surveillance data (N Engl J Med 2011 May 26;364(21):2016).
    • In patients >16 years old with bacterial meningitis in the United States, 72% of all cases are reported to be caused by Streptococcus pneumoniae while 11% are caused by Neisseria meningitidis.
      1
  • Europe:
    • STUDY SUMMARY
      overall incidence of bacterial meningitis decreasing in Netherlands since the introduction of vaccines, with most significant decrease observed in preschool and school-aged children
      POPULATION-BASED SURVEILLANCE: Clin Infect Dis 2021 Sep 7;73(5):e1099

  • United Kingdom:
    • STUDY SUMMARY
      overall incidence of bacterial meningitis in United Kingdom remained stable between 2012 and 2019, with highest incidence in infants aged < 3 months
      POPULATION-BASED SURVEILLANCE: Lancet Reg Health Eur 2023 Sep;32:100692Full Text

Risk Factors

  • Risk factors for bacterial meningitis include:
    • Abnormal communication between nasopharynx and subarachnoid space due to:
      • Congenital anatomic abnormality
      • Trauma
      • Reference - Cleve Clin J Med 2012 Jun;79(6):393
    • Externally communicating dural fistula or other dural defects
      2
      ,
      4
      ,
      6
    • Immunosuppression (particularly for asplenic patients or those with immunoglobulin deficiencies)
      4
      ,
      6
    • Older age
      1
    • Parameningeal sources of infection such as:
      • Otitis
      • Sinusitis
      • Mastoiditis
      • Odontogenic infection
      • References -
        4
        ,
        6
        , Medicine (Baltimore) 2023 Jul 7;102(27):e34177
    • Prior neurosurgery
      4
      ,
      6
    • Skull fracture
      3
      ,
      6
    • Pneumonia
      4
    • Cochlear implants (Curr Opin Otolaryngol Head Neck Surg 2014 Oct;22(5):359)
    • Living and social situations involving a high-likelihood of close-person-to-person contact (such as living in college dorms or military barracks), which is associated with an increased risk of invasive meningococcal disease (see Meningococcal Disease for additional information)
    • STUDY SUMMARY
      stress-related disorders associated with increased risk of meningitis
      COHORT STUDY: BMJ 2019 Oct 23;367:l5784

    • STUDY SUMMARY
      current opioid use associated with increased invasive Streptococcus pneumoniae infection
      CASE-CONTROL STUDY: Ann Intern Med 2018 Mar 20;168(6):396

Etiology and Pathogenesis

Causes

  • Causes for bacterial meningitis in immunocompetent adults:
    1
    ,
    6
    • Approximately 80% are caused by Streptococcus pneumoniae or Neisseria meningitidis.
    • Other organisms include Listeria monocytogenes and Staphylococci.
    • < 10% of cases are due to gram-negative bacilli including:
      • Escherichia coli
      • Klebsiella
      • Enterobacter
      • Pseudomonas aeruginosa
  • Most common causes for bacterial meningitis in immunocompromised adults:
    6
    • S. pneumoniae
    • L. monocytogenes
    • Gram-negative bacilli such as P. aeruginosa
  • There is mixed bacterial infection in < 1% of all cases of community-acquired bacterial meningitis.
    6
  • Common pathogens in neurosurgical infections:
    2
    ,
    6
    • Staphylococcus aureus or coagulase negative staphylococci, including methicillin-resistant strains
    • Gram-negative bacilli (especially Enterobacteriaceae)
  • Other bacteria:
    2
    • Haemophilus influenzae:
      • Significant cause of meningitis (especially in infants and children) before widespread immunization.
      • Incidence of nontype b strains (types e and f) has increased.
    • Streptococcus suis:
      • Occurs in parts of Asia, especially Vietnam and Thailand.
      • Increased risk in people with close contact to pigs or pork.
      • > 50% of survivors develop some degree of hearing loss.
  • STUDY SUMMARY
    Streptococcus pneumoniae most common cause of bacterial meningitis in United States in 2010
    COHORT STUDY: Lancet Infect Dis 2014 Sep;14(9):813

  • STUDY SUMMARY
    following exclusion of coagulase-negative staphylococci, Streptococcus pneumoniae, Neisseria meningitidis, and Staphylococcus aureus were leading causes of laboratory-confirmed bacterial meningitis in the United Kingdom between 2012 and 2019; among infants aged < 3 months who are most affected by bacterial meningitis, S. pneumoniae and group B Streptococcus are the most common causes of bacterial meningitis
    POPULATION-BASED SURVEILLANCE: Lancet Reg Health Eur 2023 Sep;32:100692Full Text

  • STUDY SUMMARY
    Streptococcus pneumoniae caused more than half of all bacterial meningitis in the Netherlands between 2014 and 2019, followed by Neisseria meningitidis, Haemophilus influenzae, and Streptococcus agalactiae(group B Streptococcus)
    POPULATION-BASED SURVEILLANCE: Clin Infect Dis 2021 Sep 7;73(5):e1099

Pathogenesis

  • Although much of the pathogenesis of community-acquired bacterial meningitis is not well understood, four main steps have been described:
    2
    ,
    4
    • Colonization - bacteria that cause meningitis often first colonize respiratory tract mucous membranes
    • Invasion into blood stream - pathogens may enter the bloodstream by traversing through cells (transcellularly) or between cells (pericellularly)
    • Survival in bloodstream - immune evasion is required for bloodstream survival
    • Entry into subarachnoid space - most commonly occurs following bacteremia, but direct entry into the central nervous system may be possible
  • Mechanisms of central nervous system entry:
    2
    ,
    6
    • In patients with community acquired bacterial meningitis:
      • Many bacteria associated with bacterial meningitis are capable of nasopharyngeal colonization, which can lead to blood stream invasion and bacteremia.
      • Only certain bacteria can cross the blood-brain barrier and enter the subarachnoid space, such as Neisseria meningitidis and Streptococcus pneumoniae.
      • Direct spread to the central nervous system is also likely to occur, as suggested by the high incidence of pneumococcal meningitis in patients with sinusitis and otitis media.
      • Direct entry through dural defects is also possible.
    • Nosocomial meningitis occurs when surgical manipulation or penetration of the subarachnoid space results in inoculation of pathogenic organisms.
  • Bacterial multiplication in the subarachnoid space ultimately causes a release of proinflammatory mediators, a breakdown of the blood-brain barrier, and a recruitment of leukocytes to the subarachnoid space.
    2
    ,
    6
  • Inflammation and neurological damage is caused by a combination of host and bacterial factors.
    2
    ,
    6
    • Bacterial invasion of the subarachnoid space results in the release of pro-inflammatory cytokines and consequent inflammation of the subarachnoid space (which may result in fever and headache).
    • Cytokines and other chemical mediators induce subpial encephalopathy (which may result in meningismus, confusion, reduced cerebrospinal fluid [CSF] glucose).
    • Breakdown in the blood-brain barrier and the transendothelial migration of leukocytes can lead to cerebral edema (which may result in impaired consciousness, elevated CSF pressure, increased CSF protein, focal symptoms).
    • Impaired cerebral blood flow, rising intracranial pressure, and vasculitis may cause obtundation, seizures, focal neurologic symptoms, and signs (such as cranial nerve palsies).
    • Focal neuronal injury may cause paralysis, cognitive impairment, coma, and possibly death in untreated cases.
  • Higher levels of inflammatory cytokines (common in pneumococcal meningitis) could result in a worse prognosis.
    2
Next Section >

Published by EBSCO Information Services. Copyright © 2025, EBSCO Information Services. All rights reserved. No part of this may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission.

EBSCO Information Services accepts no liability for advice or information given herein or errors/omissions in the text. It is merely intended as a general informational overview of the subject for the healthcare professional.

DynaMed Levels of Evidence

Quickly find and determine the quality of the evidence.

DynaMed provides easy-to-interpret Level of Evidence labels so users can quickly find and determine the quality of the best available evidence. Evidence may be labeled in one of three levels:

1Level 1 (likely reliable) Evidence
Representing research results addressing clinical outcomes and meeting an extensive set of quality criteria which minimizes bias.
There are two types of conclusions which can earn a Level 1 label: levels of evidence for conclusions derived from individual studies and levels of evidence for conclusions regarding a body of evidence.
2Level 2 (mid-level) Evidence
Representing research results addressing clinical outcomes, and using some method of scientific investigation, but not meeting the quality criteria to achieve Level 1 evidence labeling.
3Level 3 (lacking direct) Evidence
Representing reports that are not based on scientific analysis of clinical outcomes. Examples include case series, case reports, expert opinion, and conclusions extrapolated indirectly from scientific studies.

Grades of Recommendation

Guideline producers are now frequently using classification approaches for their evidence and recommendations, and these classifications are recognized and requested by guideline users. When summarizing guideline recommendations for DynaMed users, the DynaMed Editors are using the guideline-specific classifications and providing guideline classification approach when this is done.

Download the full version of Levels of Evidence