Meningitis/Encephalitis

Question 1

Common organisms in meningitis

Answer 1

Adults <60

• Streptococcus pneumoniae
• Neisseria meningitides
• Less common: H influenza, L. monocytogenes, S. agalactiae

Adults <>60

• Streptococcus pneumoniae
• Listeria monocytogenes
• Less common: N. meningitides, S. agalactiae, H influenza

Question 2

Clues to pathogen in meningitis:

Answer 2

• Pneumococcal → predisposing coniditions (otitis media, sinusitis, mastroiditis, CSF leak, cochlear implants, asplenia, HIV/AIDs, immunosuppressed)
• Meningococcal → young adults without comorbidities (abscence of rash not useful in excluding diagnosis)
• Listeria → consider if immunosuppressed, diabetic, alcoholic, cirrhosis, ESRF, malignancy, HIV/AIDs, organ transplantation

Question 3

CSF interpretation in bacterial meningitis:

Answer 3

• Gram stain positive in 60%
• Protein >1g/L
• CSF-blood glucose ratio ≤0.5
• WCC count >1000 (>50% PMNs). Caveats:
  
  • 10% bacterial meningitis bases WCC<100
  • Listeria meningitis may be lymphocytic
  • Viral meningitis may be neutrophilic in first 48 hours
• S. pneumoniae antigen → specificity ≥95%, sensitivity ≥85% (better than gram stain and culture)
• PCR panel:
  
  • N. meningitides, S. pneumoniae, L.monocytogenes, enterovirus, HSV and VZV
    
    • Pre-antibiotics >95% sensitivity

Question 4

Role of dexamethasone in bacterial meningitis:

Answer 4

• Benefit in pneumococcal meningitis
  
  • Reduces mortality and hearing loss and other neurological sequelae
• Reduces neuronal damage by → reducing CNS inflammation, oedema, ICP, and reducing inflammatory response from antibiotic-mediated bacteriolysis → should be given before or with first dose of antibiotics
• 10mg IV Q6H for 4/7
• Not harmful in menigococcal meningitis - but can be stopped when confirmed

Question 5

Empiric treatment of bacterial meningitis

Answer 5

• Ceftriaxone will cover all strains of N.mengitides and most strains of strep pneumoniae
• Likely that ceftriaxone still safe in penicillin allergy but moxifloxacin is an alternative
• If risk of ceftriaxone resistant strep. pneumoniae → add vancomycin
  
  • 3% in Auckland in 2018
• Penicillin or co-trim if at risk of listeria

Question 6

Infection control precautions for N.meningitides and post-exposure propylaxis

Answer 6

• Droplet precautions until 24 hours of effective antibiotics administered
• PEP for household contacts and HCWs who have performed airway management without a mask
  
  • Rifampicin 600mg PO BD for 4 doses/Ciprofloxacilin 500mg once only
  • Ceftriaxone 250mg IM preferred in pregnancy

Question 7

Notes on Japenese Encephalitis Virus → epidemiology, virology, natural course and diagnostic testing and treatment

Answer 7

• Single stranded RNA mosquito borne flavivirus - Australia outbreak 2022
• Most cases are asymptomatic or cause a non-specific febrile illness
  
  • <1% neuroinvasive disease
  • Mortality 20-30% in hospitalised patients, long term sequelae 30-50%. Most important cause of viral encephalitis in Asia and the Western Pacific.
• Disease course post incubation (5-15 days)
  
  • Initial symptoms non-specific → mental state changes, focal neurological deficits (paresis, hemoplegia, tetraplegia or CN palsies) and or movement disorders
  • Poor prognostic factors → multiple seizures and raised ICP, flexor and extensor posturing, abnormal pupillary and oculocephalic reflexes
• Diagnostic testing → serological testing of IgM in the CSF or serum, viral isolation confirmatory but rare. MRI → changes in the thalamus (most common), basal ganglia, midbrain, pons and medulla
• Treatment → supportive
• Vaccine → those who work with pigs, mosquitos, research staff who may be exposed