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Year 5 Microbiology > 7: CNS Infections and Meningitis > Flashcards

7: CNS Infections and Meningitis Flashcards

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1
Q

4 routes of Pathogen Entry into the CNS

A

Haematogenous (e.g. pneumococcus, meningococcus)

  • MOST COMMON
  • causes of aseptic meningitis include enterovirus and herpes (also transfers via haematogenous spread)

Direct implantation (e.. trauma)

Local extension (e.g. from the ear)

PNS into CNS (e.g. rabies)

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2
Q

Meningitis vs Encephalitis

A
  • Meningitis = “I don’t know who the prime minister is” but all other AMTS fine
  • Encephalitis = “Tony Blair is the prime minister and I’m in the secret service”
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3
Q

4 main symptoms once pathogens enter CNS

A
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4
Q

What is meningitis and meningoencephalitis

A

Meningitis = inflammatory process of the meninges and CSF

Meningoencephalitis = inflammation of the meninges and brain parenchyma

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5
Q

Neurological damage in meningitis

A

(10% mortality, 5% have neurological sequelae; sensorineural deafness) is caused by:

  • Direct bacterial toxicity
  • Indirect inflammatory process and cytokine release and oedema (n.b. tight space, oedema = bad)
  • Shock, seizures and cerebral hypoperfusion
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6
Q

Classification of meningitis

A
  • Acute (hours to days)
  • Chronic (days to weeks)
  • Aseptic (caused by viruses so there is no pus)
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7
Q

3 main causes of acute meningitis

A

Neisseria meningitidis

  • ≥12 serotypes (90% = A, B, C); A, B, C, W and Y are vaccinated against
  • Transmitted from person-to-person, from asymptomatic carriers
    • Pathogenic strains are only found in about 1% of carriers
      • Enters the body through the nasopharyngeal mucosa in a susceptible individual
      • Causes infection in <10 days
        • Non-blanching rash (80% of children)
        • Maculopapular rash (13% of children)
        • No rash (7% of children)
      • 50% have meningitis, 7-10% have septicaemia, 40% have meningitis AND septicaemia
        • Important to distinguish as treatment for shock and raised ICP is different *

Streptococcus pneumoniae

  • Bimodal distribution (children, elderly)

Haemophilus influenzae

  • Type B is immunised against
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8
Q

Other and rare causes of meningitis

A

Other causes:

  • Listeria monocytogenes (key cause of meningoencephalitis)
  • Group B Streptococcus (can cause neonatal meningitis)
  • Escherichia coli (biphasic – old people and neonates)

Rare causes:

  • TB, S. aureus, T. pallidum, Cryptococcus neoformans
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9
Q

4 processes of septicaemia

A

Capillary Leak – albumin and other plasma proteins leads to hypovolaemia

Coagulopathy – leads to bleeding and thrombosis (endothelial injury results in platelet release reactions, the protein C pathway and plasma anticoagulants are affected)

Metabolic Derangement – particularly acidosis

Myocardial failure – and multi-organ failure

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10
Q

Chronic meningitis presentation, epidemiology and complications

A

(e.g. Tuberculous chronic meningitis) – may take weeks to develop:

  • Similar presentation to acute meningitis (fever, headache, neck stiffness) but lower mortality (0.000055%)
  • More common in immunosuppressed patients
  • Involves the meninges and basal cisterns of the brain and spinal cord with dilatation of ventricles

Complications:

  • Tuberculous granulomas
  • Tuberculous abscesses (i.e. enhancing thick-walled abscesses)
  • Cerebritis
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11
Q

Aseptic meningitis

A

MOST COMMON infection fo the CNS

  • Presentation: headache, stiff neck, photophobia
  • A non-specific rash may accompany these symptoms
  • Organisms (80-90% of organisms) – VIRAL:
    • Coxsackie group B
    • Echoviruses

Usually occurs in children <1 year

Self-limiting disease that resolves in 1-2 weeks

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12
Q

Aseptic meningitis

A

MOST COMMON infection of the CNS

  • Presentation: headache, stiff neck, photophobia
  • A non-specific rash may accompany these symptoms
  • Organisms (80-90% of organisms) – VIRAL:
    • Coxsackie group B
    • Echoviruses

Usually occurs in children <1 year

Self-limiting disease that resolves in 1-2 weeks

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13
Q

Encephalitis transmission

A
  • Transmission is pretty much ALL haematogenous:
    • Person-to-person
    • Vectors (e.g. mosquitoes, lice, ticks)
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14
Q

Causes of viral encephalitis

A

UK = HSV-2

WW = arboviruses

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15
Q

Importance of West Nile virus

A
  • IMPORTANT: West Nile Virus is becoming a leading cause of encephalitis worldwide
    • Mainly transferred by mosquitoes and birds (European birds spend the winter in Southern Europe and Africa)
    • West Nile Virus has spread across the USA but hasn’t reached the UK yet
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16
Q

Non-viral encephalitis examples

A
17
Q

2 types of focal CNS infections

A

Brain Abscesses and Spinal infections

18
Q

How does brain abscess cause death

what do brain abscesses look like on MRI

A

Death due to pressure-related issues

19
Q

Brain abscess how does it infect

A
  • Direct extension (e.g. otitis media, mastoiditis, para-nasal sinuses)
  • Occasionally spread haematogenously (e.g. endocarditis)
20
Q

Causative organisms for brain abscesses

A

Causative Organisms (Strep > Staph > gram -ve > other):

  • Streptococci (anaerobic and aerobic)
  • Staphylococci
  • Gram-negative organisms (mainly in neonates)
  • TB, fungi, parasites, actinomyces and Nocardia species
21
Q

Most common form of spinal infections and route of spread

A

Pyogenic vertebral osteomyelitis is a common form of vertebral infection (e.g. staph and strep)

Spread via… direct open spinal trauma or it can spread haematogenously

22
Q

Complications of untreated spinal infections

A
  • Permanent neurological deficits
  • Significant spinal deformity
  • Death
23
Q

RFs for spinal infections

A
  • Age IVDU Long-term systemic steroids
  • Diabetes mellitus Organ transplantation Malnutrition
  • Cancer
24
Q

Diagnostics for CNS infections

A
25
Q

CSF results

A
26
Q

Examples of pathogens

A

Gram +ve cocci

  • S. Pneumonia
  • A-haemolytic diplococcus

Gram +ve rod

  • L. monocytogenes

Gram -ve cocci

  • Gram-ve diploccocus
  • N. meningitides
27
Q

Rare pathogen causing meningitis

A
  • Hx: MSM, 3/7 history
  • High opening pressure on LP
  • HOP pathogenomic of C. neoformans
  • Occurs in immunocompromised people
28
Q

Limitations of diagnostics

A
  • MRI oedema pattern and moderate mass effect cannot be differentiated from tumour or stroke or vasculitis
  • Serology may not be useful in early stages of infection
  • Difficulties obtaining sufficient CSF
  • PCR techniques are expensive
  • Methods to detect amoebic infections
  • Availability of good laboratory technique
29
Q

Mx approach to patients with possible CNS infection

A
30
Q

Menignitis vs meningo-encephalitis treatment

A
  • Ceftriaxone is good at killing N. meningitidis, S. pneumoniae, HiB and E. coli
    • However, Ceftriaxone does NOT cover Listeria monocytogenes  this requires amoxicillin
    • Hence why, if >50yo, treat with amoxicillin
31
Q

Specific therapies to meningitis pathogens

A
32
Q

Adjunctive therapy

A
  • Level of care required
  • Corticosteroids (do NOT give them without speaking to a specialist, but it can be useful for cerebral oedema)
  • Repeat LP
  • Public health
33
Q

Key take-home messages

A
  • Act fast in CNS infections
  • Take appropriate samples
  • Anticipate the likely microbiology – this directly impacts empirical antimicrobial therapy
  • Learn the CSF interpretation table by rote – this directly impacts refining the antimicrobial therapy
34
Q

Examples of pathogens

A

Gram +ve cocci

  • S. Pneumonia
  • A-haemolytic diplococcus

Gram +ve rod

  • L. monocytogenes

Gram -ve cocci

  • Gram-ve diploccocus
  • N. meningitides

Year 5 Microbiology (8 decks)

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