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ContentsSynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyReferencesView all Images (3)
Potentially life-threatening emergency
Bacterial meningitis in Adult
Other Resources UpToDate PubMed
Potentially life-threatening emergency

Bacterial meningitis in Adult

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Contributors: Shiven B. Chabria MD, Mukesh Patel MD
Other Resources UpToDate PubMed


Meningitis is characterized by cerebrospinal fluid (CSF) pleocytosis and a clinical symptom complex of fever, headache, and meningismus. It represents acute purulent infection of the subarachnoid space. The etiologies of meningitis are myriad, with bacteria, viruses, fungi, parasites, and noninfectious causes all being implicated. In addition to community-acquired infection, nosocomial bacterial meningitis should be considered in patients with invasive procedures, complicated head trauma, or systemic bacteremia. This summary will highlight bacterial pathogens as the etiologic agents of acute meningitis.
While cases of bacterial meningitis have decreased over the past several decades as a result of use of Haemophilus influenzae type b conjugate vaccine and polysaccharide pneumococcal vaccine, contemporary studies suggest the incidence is 4-6 cases per 100 000 adults and as high as 80 cases per 100 000 infants younger than 2 months of age. The 3 most common pathogens, H. influenzae, Neisseria meningitidis, and Streptococcus pneumoniae, account for >80% of cases in the adult population. Group B Streptococcus (GBS) accounts for the majority of infections in infants younger than 2 months of age. Mortality is higher for pneumococcal meningitis (as high as 30%) versus non-pneumococcal meningitis (7%-11%).

Antecedent history of otitis media, upper respiratory tract infection, pneumonia, gastrointestinal symptoms, or trauma may provide an indication to possible etiologic agents.

Neisseria meningitidis can cause characteristic skin manifestations such as petechiae and palpable purpura.

Patients with Listeria meningitis have an increased risk of seizures and focal neurological deficits early in the course of infection. Rhombencephalitis can occur, manifested as ataxia with cranial nerve palsies and/or nystagmus. Consumption of undercooked or improperly refrigerated food has been linked to sporadic Listeria outbreaks.

Acute bacterial meningitis may manifest as meningitis or meningoencephalitis with or without accompanying sepsis. The classic triad of acute meningitis includes fever, neck stiffness, and altered mental status. These 3 findings at presentation are found in only 44% of patients. However, at least 2 of 4 findings of headache, fever, stiff neck, and altered mentation are seen in 95% of patients. Altered mental status is present in almost two-thirds of patients with bacterial meningitis and is usually absent in viral meningitis unless coincident encephalitis is present. Lethargy or altered level of consciousness is more common in acute bacterial meningitis, with coma seen in up to 20% of patients. Depression of sensorium occurs more commonly with pneumococcal rather than meningococcal meningitis.

Focal cerebral abnormalities to consider include hemiparesis, monoparesis, and aphasia and may be due to stroke, seizures, or both. Cranial nerve palsies may occur, with eighth nerve palsy being most common.

The 3 clinical features on presentation that portend an adverse outcome appear to be the presence of hypotension, altered mental status, and seizures.

Common acute meningitis bacterial pathogens by risk factor:
Age <1 month:
  • GBS
  • Escherichia coli
  • Listeria monocytogenes
  • Klebsiella spp.
Age 1-23 months:
  • Streptococcus pneumoniae
  • Neisseria meningitidis
  • GBS
  • Haemophilus influenzae
  • Escherichia coli
Age 2-50 years:
  • Neisseria meningitidis
  • Streptococcus pneumoniae
Age >50 years:
  • Streptococcus pneumoniae
  • Neisseria meningitides
  • Listeria monocytogenes
  • Aerobic gram-negative bacilli
Basilar skull fracture:
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Group A beta-hemolytic streptococci
Penetrating skull fracture:
  • Staphylococcus aureus
  • Coagulase-negative staphylococci
  • Aerobic gram-negative bacilli (including Pseudomonas aeruginosa)
  • Aerobic gram-negative bacilli (including P. aeruginosa)
  • Staphylococcus aureus
  • Coagulase-negative staphylococci
CSF shunt:
  • Coagulase-negative staphylococci
  • Staphylococcus aureus
  • Aerobic gram-negative bacilli (including P. aeruginosa)
  • Propionibacterium acnes
  • Streptococcus pneumoniae
  • Neisseria meningitides
  • Listeria monocytogenes
  • Aerobic gram-negative bacilli


G00.9 – Bacterial meningitis, unspecified

95883001 – Bacterial meningitis

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Viral meningitis – Culture negative, lymphocytic pleocytosis (when present) with normal CSF glucose. CSF viral polymerase chain reaction (PCR) testing may establish the diagnosis.
  • Drug-induced aseptic meningitis – Many drugs implicated, especially nonsteroidal anti-inflammatory drugs, antibiotics, OKT3 monoclonal antibodies, and intravenous immunoglobulin. Neutrophils or lymphocytes can dominate CSF, occasionally eosinophils seen.
  • Paraneoplastic syndrome – Many tumors have been associated with auto-antibody production resulting in meningoencephalitis. CSF and serum testing for antibodies establishes the diagnosis.
  • Subdural empyema – Suggested by rapid deterioration; associated sinus or mastoid infection or surgery.
  • Subarachnoid hemorrhage – Look for the presence of red blood cells (RBC) and xanthochromia on CSF.
  • Stroke – Large strokes may cause meningeal irritation if there is significant necrosis in the brain or hemorrhage. Temporally, the fevers usually present 24-48 hours after stroke.
  • Delirium tremens – Patients can have confusion, fevers, and rigidity. History of alcohol use, negative cultures, and otherwise bland CSF point toward the diagnosis.
  • Brain abscess – Symptoms may include headache, fever, and focal neurologic findings.
  • Paravertebral or epidural abscess – Local inflammation my produce CSF pleocytosis without actual infection of the CSF. Imaging the spine may identify lesion.
  • Autoimmune cerebritis (see antibody-mediated encephalitis) – Acute meningoencephalitis can occur with autoimmune disease, particularly sarcoidosis and systemic lupus erythematosus. Angiography may reveal vasculitis, CSF is sterile.

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Last Updated: 09/06/2018
Copyright © 2018 VisualDx®. All rights reserved.
Potentially life-threatening emergency
Bacterial meningitis in Adult
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Bacterial meningitis : Altered mental state, Severe headache, CSF glucose low, CSF protein elevated, Patient appears systemically ill - toxic, Nuchal rigidity, Lethargy, Increased white blood cell count in CSF, High fever
Clinical image of Bacterial meningitis
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