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Medical Microbiology Exam > Meningitis > Flashcards

Meningitis Flashcards

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1
Q

What age groups are susceptible to meningitis?

A

All age groups, but infants, young children, and the elderly are most susceptible

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2
Q

What is the most common cause of meningitis?

A

Viral meningitis

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3
Q

How many cases of viral meningitis occurred from 2009-10?

A

3000 reported cases (actual incidence is likely to be far higher)

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4
Q

How many cases of bacterial meningitis occur in the UK per year?

A

~3200

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5
Q

How many cases of encephalitis occur in the UK per year?

A

~4400

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6
Q

During CNS invasion, where does blood-borne invasion take place?

A

Across the blood-brain barrier to cause encephalitis

Across the blood-brain-cerebrospinal fluid barrier to cause meningitis

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7
Q

What is the blood-brain barrier?

A

Barrier of tightly joined endothelial cells surrounded by glial processes

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8
Q

What is the blood-brain-cerebrospinal fluid barrier?

A

Barrier of endothelium fenestrations and tightly joined choroid plexus epithelial cells

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9
Q

How can microbes traverse the blood-brain and blood-brain-cerebrospinal fluid barriers?

A

Growing across, infecting cells that make up the barrier
Passively transported across in intracellular vacuoles
Carried across by infected WBCs

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10
Q

Give examples of how viruses can invade the CNS

A

Herpes simplex, varicella-zoster and rabies can invadethe CNS via peripheral nerves

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11
Q

In what ways can the CNS be invaded by microbes?

A

Microbes can traverse the BBB and BBCSF barriers (often after invasion of the blood stream)
Viruses can invade the CNS via the peripheral nerves
Direct contiguous spread can occur

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12
Q

What can cause direct contiguous spread into the CNS?

A 
Sinusitis
Otitis media
Congenital malformations
Trauma
Direct inoculation during intracranial manipulation (via the Olfactory portal)
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13
Q

What are the common causes of Meningitis?

A 
Neisseria meningitidis (A, B, C, Y, W-135) (up to 20% carriage)
Streptococcus pneumoniae
Group B streptococcus
Haemophilus influenzae B
Listeria monocytogenes
Gram negatives
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14
Q

What bacteria can cause chronic meningitis?

A 
Mycobacterium tuberculosis
Mycobacterium avium
Treponema pallidum
Brucellosis
Nocardia sp
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15
Q

What fungi can cause chronic meningitis?

A

Cryptococcus neoformans
Candida sp.
Aspergillus sp

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16
Q

What parasites can cause chronic meningitis?

A 
Taenia solium (beef tapeworm)
Toxoplasma gondii
17
Q

What virulence factors does Neisseria meningitidis possess?

A 
Capsule
IgA protease
Pili
Endotoxin
Outer membrane proteins
18
Q

What virulence factors does Haemophilus influenzae possess?

A 
Capsule
IgA protease
Pili
Endotoxin
Outer membrane proteins
19
Q

What virulence factors does Streptococcus pneumoniae possess?

A

Capsule

IgA protease

20
Q

During meningitis infection, what occurs as a result of damage due to inflammation?

A

Vascular endothelial injury and increased blood-brain barrier permeability leads to entry of many blood components into the subarachnoid space
Neutrophils migrate from the bloodstream and penetrate the damaged blood-brain barrier, leading to profound neutrophilic pleocytosis
Vasogenic oedema and elevated CSF protein levels

21
Q

How does meningitis pathogenesis progress?

A

In less severe cases the inflammatory process remains confined to the subarachnoid space and the pial barrier is not penetrated, and the underlying parenchyma remains intact
In more severe forms of bacterial meningitis, the pial barrier is broken, and the underlying parenchyma is invaded by the inflammatory process
Exudates extend throughout the CSF, particularly to the basal cisterns, damaging cranial nerves (eg, cranial nerve VIII, with resultant hearing loss), obliterating CSF pathways (causing obstructive hydrocephalus), and inducing vasculitis and thrombophlebitis (causing local brain ischemia)
Bacterial meningitis may lead to widespread cortical destruction, particularly when left untreated

22
Q

What are the risk factors for Neisseria meningitidis?

A

Complement defects:
- Properdin defects
- Deficiencies in terminal complement components (e.g. membrane attack complex, C5-C9); *surprisingly associated with lower mortality rates
Previous viral infection, chronic medical illness, corticosteroid use, and active or passive smoking
Overcrowding e.g university halls and military facilities

23
Q

What are the symptoms of meningitis?

A

Headache: 75-90%
Photophobia: uncommon

On examination:
Fever: 95%
Stiff Neck: 85%
Altered mental status: 80%
All three: 40%
Any one of the three: 100%

Symptoms develop with hours or within 1 to 2days
Non-blanching rash is seen classically with N. meningitidis but can occur with other bacterial and viral infections
Endotoxic shock with vascular collapse is characteristic of severe N. meningitidis infection
Altered mental status, from irritability to somnolence, delirium, and coma, can develop

24
Q

What complications can occur with meningitis infection? (12)

A 
Hearing loss
Cortical blindness
Other cranial nerve dysfunction
Paralysis
Muscular hypertonia
Ataxia
Multiple seizures
Mental motor retardation
Focal paralysis
Subdural effusions
Hydrocephalus
Cerebral atrophy
25
Q

What are the mortality rates of meningitis?

A

N. meningitidis 3-13%
S. pneumoniae 19-26%
H. influenzae 3-6%
L. monocytogenes 15-29%

Patients with meningococcal meningitis have a better prognosis (mortality rate of 4-5%) than do those with pneumococcal meningitis
Patients with meningococcemia have a poor prognosis, with a mortality rate of 20-30%

26
Q

What is the treatment recommended for bacterial meningitis in patients aged 3 months - 50 years?

A

Ceftriaxone or cefotaxime plus vancomycin

*Vancomycin is added to the initial regimen if the presence of penicillin-resistant S. pneumoniae is suspected or if a high incidence of resistance is reported in the community

27
Q

What tests are performed if a diagnosis of meningitis is suspected?

A

CSF:

  • Complete cell count
  • Differential leucocyte count
  • Examination of Gram stained smear
  • Determination of glucose and protein concentrations in CSF (clinical biochemistry)
  • Latex antigen test
  • Culture
  • PCR

Blood:

  • Full blood count
  • Haematocrit
  • Culture
28
Q

What is the purpose of a CSF gram stain?

A

CSF Gram stain permits rapid identification of the bacterial cause in 100% specific 60-90% sensitivity

29
Q

When is a CSF acid fast stain performed?

A

Acid fast stain if M. tuberculosis or M. avium is suspected

30
Q

Give examples of what can be seen with a CSF gram stain

A

Streptococcus pneumoniae - Gram positive cocci in singles and pairs
Neisseria meningitidis - Gram negative diplococci in singles and pairs
Haemophilus influenzae - Gram negative coccobacilli Listeria monocytogenes - Gram positive rods

31
Q

How are samples cultured if meningitis is suspected?

A

Blood/chocolate agar
Incubated with 5% CO2
18- 24 h at 35-37oC

Medical Microbiology Exam (3 decks)

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