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BASICS

Bacterial meningitis is a bacterial infection of the meninges causing inflammation, pain, and systemic illness.

EPIDEMIOLOGY

  • Age groups: neonates, infants, elderly
  • Sex: male = female
  • Incidence varies by age and pathogen:
  • 18-34 years: 0.66/100,000
  • 35-49 years: 0.95/100,000
  • 50-64 years: 1.73/100,000
  • ≥65 years: 1.92/100,000
  • Pathogen incidence:
  • Group B Streptococcus: 0.25/100,000
  • Neisseria meningitidis: 0.19/100,000
  • Haemophilus influenzae type B: 0.08/100,000
  • Listeria monocytogenes: 0.05/100,000
  • Prevalence: 15,000 to 25,000 cases annually in the U.S.

ETIOLOGY AND PATHOPHYSIOLOGY

  • Common causes:
  • Community-acquired: Streptococcus pneumoniae (50%), Neisseria meningitidis (30%)
  • Nosocomial/postsurgical: manipulation of CNS
  • Age-specific pathogens:
  • Newborns (<2 months): group B Streptococcus, E. coli, L. monocytogenes
  • Infants/children: S. pneumoniae, N. meningitidis, H. influenzae
  • Adolescents/young adults: N. meningitidis, S. pneumoniae
  • Immunocompromised adults: S. pneumoniae, L. monocytogenes, gram-negative bacilli (Pseudomonas aeruginosa)
  • Older adults: S. pneumoniae 50%, N. meningitidis 30%, L. monocytogenes 5%, gram-negative bacilli 10%
  • Genetics: Some Native American populations have genetic susceptibility.

RISK FACTORS

  • Close contacts of case patients
  • Immunocompromised (HIV, asplenia, eculizumab/ravulizumab use)
  • Alcohol use disorder, diabetes, chronic disease
  • Neurosurgery, head injury
  • Close living quarters (dormitories, military barracks)
  • Neonates: prematurity, low birth weight, PROM, maternal infections, urinary abnormalities
  • Anatomical abnormalities (nasopharynx, subarachnoid space)
  • Parameningeal sources: otitis, sinusitis, mastoiditis, skull fracture
  • Elderly, pregnant at risk for listeriosis
  • Complement deficiencies (properdin, factor H, factor D)

GENERAL PREVENTION

  • Consider CSF fistula in recurrent meningitis
  • Aseptic technique for head wounds/skull fractures
  • Vaccination: H. influenzae type B, pneumococcal conjugate vaccines
  • Chemoprophylaxis for close contacts of meningococcal patients

COMMONLY ASSOCIATED CONDITIONS

  • Worse prognosis: alcohol use disorder, elderly, infancy, diabetes, multiple myeloma, head trauma, seizures, immunocompromised, coma, sepsis, sinusitis

DIAGNOSIS

HISTORY

  • Antecedent upper respiratory infection
  • Fever, headache, vomiting, photophobia, seizures, confusion
  • Nausea, rigors, sweats, weakness
  • Elderly: subtle confusion
  • Infants: irritability, lethargy, poor feeding, altered mental status
  • Food exposures (e.g., L. monocytogenes)

PHYSICAL EXAM

  • ≥95% present with ≥2 of: headache, fever, neck stiffness, altered mental status
  • Meningismus, focal neurologic deficits
  • Meningococcal rash: macular → petechial/purpuric, purpura fulminans
  • Papilledema
  • Brudzinski sign: passive neck flexion → involuntary knee flexion
  • Kernig sign: resistance/pain on knee extension after hip flexion
  • Late signs: hemiparesis, stroke, cognitive impairment, coma, epilepsy, hearing/visual loss

DIFFERENTIAL DIAGNOSIS

  • Bacteremia, sepsis, brain abscess, seizure
  • Nonbacterial meningitis
  • Inflammatory/autoimmune: Behçet disease, SLE, sarcoidosis, migraine
  • Stroke, viral meningitis, Lyme disease, leptospirosis
  • Subarachnoid hemorrhage
  • CNS vasculitis

DIAGNOSTIC TESTS & INTERPRETATION

Initial Tests

  • Lumbar puncture: prompt unless contraindicated
  • Head CT: before LP if focal neuro deficits, papilledema, altered mentation
  • CSF: turbid; Gram stain, cultures
  • Adults: WBC >500 cells/mL, glucose <40 mg/dL, CSF protein >200 mg/dL
  • Opening pressure >30 cm H2O
  • PCR for viral meningitis suspicion
  • Reserve antigen tests if Gram stain and culture negative at 48h
  • CBC, blood cultures, serum electrolytes, coagulation studies
  • Chest X-ray: pneumonitis or abscess
  • CRP: normal CRP excludes bacterial meningitis
  • Repeat head CT if hydrocephalus, brain abscess, subdural complications suspected or no response after 48h

Follow-Up Tests

  • Initiate empiric antibiotics once blood cultures drawn if LP delayed

Diagnostic Procedures

  • Noncontrast CT to assess risk of herniation prior to LP in select patients
  • Lumbar puncture contraindications: signs of increased ICP, skin infection at LP site, CT/MRI showing hydrocephalus, edema, herniation
  • Positive CSF culture and pleocytosis confirms meningitis

TREATMENT

GENERAL MEASURES

  • Empiric antibiotics immediately after LP or after blood cultures if CT needed (Abx > CT > LP)【1】
  • Monitor seizures and aspiration precautions

MEDICATION

First Line:
- Neonates: ampicillin (150 mg/kg/day q8h) + cefotaxime (150 mg/kg/day q8h)
- Infants >4 weeks: ceftriaxone (100 mg/kg/day q12-24h) or cefotaxime (225-300 mg/kg/day q6-8h) + vancomycin (60 mg/kg/day q6h)
- Adults:
- Immunocompetent: cefotaxime 2 g IV q4-6h or ceftriaxone 2 g IV q12h
- If ceftriaxone resistance >1%, add vancomycin 15-20 mg/kg IV q8-12h + ampicillin 2 g IV q4h (if >50 years)
- Immunocompromised: vancomycin + ampicillin + cefepime or meropenem (no ampicillin if meropenem used)
- Penicillin allergy:
- Mild: meropenem instead of ceftriaxone
- Severe: vancomycin loading dose 25-30 mg/kg IV + moxifloxacin 400 mg IV daily
- Duration:
- S. pneumoniae: 10-14 days【2】
- N. meningitidis, H. influenzae: 7-10 days
- Group B strep, E. coli, L. monocytogenes: 14-21 days
- Neonates: 12-21 days or 14 days post sterile culture

Corticosteroids:
- Dexamethasone (0.15 mg/kg IV q6h for 2-4 days) improves mortality/morbidity in S. pneumoniae meningitis【2】
- Start 15-20 min before or with antibiotics
- Continue only if Gram stain or culture confirms S. pneumoniae

Second Line:
- Antipseudomonal penicillins + other agents (aztreonam, fluoroquinolones, meropenem) for resistant organisms

ISSUES FOR REFERRAL

  • Infectious disease and critical care consultation

ADDITIONAL THERAPIES

  • Chemoprophylaxis for close contacts (household, dormitories, military, childcare, intimate contacts) with rifampin, ciprofloxacin, ceftriaxone, or azithromycin

SURGERY/OTHER PROCEDURES

  • Postsurgical or head trauma meningitis: empiric MRSA + aerobic gram-negative coverage including Pseudomonas

ADMISSION, INPATIENT, AND NURSING CONSIDERATIONS

  • Hospitalization required
  • ICU monitoring may be necessary
  • Respiratory isolation for 24h if meningococcal infection suspected
  • Droplet precautions during first 24h of antimicrobials

ONGOING CARE

FOLLOW-UP

  • Brainstem auditory evoked response test for infants before discharge
  • Vaccinations:
  • Meningococcal (MenACWY at 11-12 y, booster at 16 y; MenB vaccine for 16-23 y; routine for at-risk ≥10 y)
  • Pneumococcal (PCV13 for infants/children; PPSV23 for adults ≥65 y and select groups)
  • Monitor for antibiotic resistance and prophylaxis failures

DIET

  • Regular diet as tolerated except for SIADH cases

PROGNOSIS

  • Mortality: S. pneumoniae 19-37%; meningococcal 5%
  • Untreated disease: mortality ~100%
  • Deaths from N. meningitidis usually within 12-24 hours of symptom onset

COMPLICATIONS

  • Up to 50% have long-term neurologic deficits (cognitive impairment) after pneumococcal meningitis
  • Seizures (20-30%), focal neurologic deficits
  • Cerebrovascular complications: subdural effusion/empyema, septic sinus thrombosis, intracranial hypertension, cerebral edema, herniation, hydrocephalus
  • Cranial nerve palsies (III, VI, VII, VIII) in 10-20%, usually transient
  • Sensorineural hearing loss (10% children)
  • Permanent visual impairment
  • Neurodevelopmental sequelae (30% subtle learning deficits)
  • Obstructive hydrocephalus, subdural effusion, SIADH, elevated ICP
  • Purpura fulminans, septic shock
  • Meningococcal microvascular thrombosis, DIC, depression, subarachnoid hemorrhage, stroke

REFERENCES

  1. Pajor MJ, Long B, Koyfman A, et al. High risk and low prevalence diseases: adult bacterial meningitis. Am J Emerg Med. 2023;65:76-83.
  2. Tunkel AR, Hartman BJ, Kaplan SL, et al. Practice guidelines for the management of bacterial meningitis. Clin Infect Dis. 2004;39(9):1267-1284.
  3. Tunkel AR, Hasbun R, Bhimraj A, et al. 2017 Infectious Diseases Society of America's clinical practice guidelines for healthcare-associated ventriculitis and meningitis. Clin Infect Dis. 2017;64(6):e34-e65.

ICD10 Codes

  • G00.9 Bacterial meningitis, unspecified
  • G00.2 Streptococcal meningitis
  • G00.8 Other bacterial meningitis

Clinical Pearls

  • Monitor prophylaxis failures and antimicrobial resistance among meningococcal isolates.
  • Empiric therapy for suspected meningococcal disease: extended-spectrum cephalosporin (e.g., cefotaxime or ceftriaxone).
  • Definitive treatment guided by microbiologic diagnosis: penicillin G, ampicillin, or extended-spectrum cephalosporin.