Meningitis
May 16, 2025
Definition
Definition and Classification
Meningitis is inflammation of the meninges and subarachnoid
space, usually infectious.
Classified by:
Duration: Acute, subacute, chronic
Etiology: Bacterial, viral, fungal, tuberculous, parasitic
Meningism: Mimics meningitis (e.g., neck stiffness) but without
true inflammation.
Meningitis
Bacterial Meninfitis
Acute Bacterial Meningitis: Epidemiology
Case fatality: 15–25%; neurologic sequelae in 25%
Epidemic rates: 12–1000/100,000
Vaccination has reduced Haemophilus and Streptococcus
pneumoniae cases
Listeria: 30–40% fatality
High-risk groups: Neonates, elderly, immunocompromised,
asplenia, skull fracture
Meningitis belt: Large outbreaks during dry season
Meningitis
Bacterial Meninfitis
Common Pathogens by Age
Age Group Common Pathogens
<1 month GBS, E. coli, Listeria monocytogenes
<2 years S. pneumoniae, N. meningitidis, GBS, H. influenzae B, E. coli
2–50 years S. pneumoniae, N. meningitidis
>50 years S. pneumoniae, N. meningitidis, Listeria, aerobic Gram-negative bacilli
Meningitis
Bacterial Meninfitis
Additional Pathogen Risks
Basilar skull fracture: S. pneumoniae, H. influenzae, S. pyogenes
Asplenia: Encapsulated organisms
Neurosurgical patients: Gram-negatives, Pseudomonas, S.
aureus
Strongyloides hyperinfection: E. coli, S. bovis
Meningitis
Bacterial Meninfitis
Clinical Features
Classic triad: Fever, headache, neck stiffness
Infants: Irritability, bulging fontanelle
Petechiae/purpura: Common in N. meningitidis
Basilar skull fracture: CSF rhinorrhea or otorrhea
Atypical in elderly/immunocompromised (confusion, lethargy)
Meningitis
Bacterial Meninfitis
CSF Analysis
Parameter Normal Bacterial Viral TB Fungal
Opening Pressure 12–20 ↑ Normal/↑ ↑ ↑
Appearance Clear Turbid Clear Clear/cloudy Clear/cloudy
WBC (/µL) <5 >100 (PMN) 5–100 (Lymph) 5–500 (Lymph) 5–500 (Lymph)
Protein (g/L) 0.4 ↑ Slight ↑ Marked ↑ ↑
Glucose ratio >2/3 Very low Normal/Slight ↓ Very low Low
Meningitis
Bacterial Meninfitis
Diagnosis and Imaging
Blood cultures before antibiotics
PCR for S. pneumoniae, N. meningitidis
CT before LP if signs of raised ICP or focal deficits
Meningitis
Bacterial Meninfitis
Empirical Antibiotics
Adults: Ceftriaxone 2g IV q12h or cefotaxime ± vancomycin
Elderly/immunocompromised: Add ampicillin 2g IV q4h
Suspected resistance: Add vancomycin (not alone)
Meningitis
Bacterial Meninfitis
Pathogen-Specific Treatment
Pathogen Treatment Duration
S. pneumoniae Penicillin G or ceftriaxone ± vancomycin 10–14 days
N. meningitidis Penicillin G or ceftriaxone 5–7 days
Listeria Ampicillin ± gentamicin ≥21 days
H. influenzae Ampicillin or ceftriaxone 7–10 days
E. coli Ceftriaxone 21 days
Meningitis
Bacterial Meninfitis
Adjuncts and Prophylaxis
Dexamethasone: 10 mg IV q6h × 4 days (for S. pneumoniae)
Stop if not pneumococcal
Prophylaxis: Ciprofloxacin 500 mg PO (alt: rifampin, ceftriaxone)
For close/intimate contacts and exposed HCWs
Meningitis
Bacterial Meninfitis
Outcomes
Children: 15% have severe sequelae
Adults: 1/3 have long-term cognitive impairment
Gram-negative meningitis: 40–80% mortality
Meningitis
Viral Meninfitis
Acute Viral Meningitis
Enteroviruses: 90% of cases
HSV-2: Recurrent meningitis
Mumps: In unimmunized
Arboviruses: Seasonal (e.g., West Nile, EEEV)
Meningitis
Viral Meninfitis
Viral Meningitis Features & Treatment
Enterovirus: Rash, diarrhea
HSV-2: Genital lesions
Primary HIV: Lymphadenopathy, rash
Treatment:
HSV-2, VZV: Acyclovir 10 mg/kg IV q8h
Severe flu: Oseltamivir 75 mg PO BID
Neonatal enterovirus: IVIG
Meningitis
TB Meningitis
Chronic TB Meningitis
High TB prevalence regions
CSF: Lymphocytes, very low glucose, high protein
MRI: Basal enhancement, hydrocephalus
Treatment:
Intensive (2 mo): RIPE + dexamethasone
Maintenance (9–12 mo): Rifampin + INH
Meningitis
