Microbiology and Immunology Flashcards by Gabriel Jones

What is meningitis?

Inflammation of the meninges

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What is encephalitis?

Inflammation of the brain parenchyma

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What is myelitis?

Inflammation of the spinal cord.

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What is neuritis?

Inflammation of the neurons/nerves.

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How many die a year from meningitis?

125,000

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Which group of people suffer the most deaths from meningitis per year?

Infants and young children

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Where is meningitis most prevalent?

In less developed countries - 96%.

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What are the two major classifications of meningitis?

Bacterial and aseptic.

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What are the two different divisions of bacterial meningitis?

Culture positive and culture negative

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Which form of meningitis is the most serious but the second most common?

Bacterial meningitis

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What are the 3 different types of aseptic (culture negative) meningitis?

Viruses, non-infectious and other (e.g. TB, fungal, etc.)

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What is the most common cause of meningitis?

Aseptic meningitis (culture negative)

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What are the most common causes of bacterial meningitis in infants, children and adults? Why?

Haemophilus influenza

Neisseria menigitidis

Streptococcus pneumoniae

Because these bacteria are best at evading the immune system.

They are encapsulated in a polysaccharide capsule, enabling them to evade the immune response, particularly complement fixation.

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What are the most common causes of bacterial meningitis in neonates/infants <3 months of age?

E. coli/other Gram negative bacilli

Group B streptococcus

Listeria monocytogenes

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What are the most common meningococcal subgroups globally?

A, C, W-135 and X

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What are the most common meningococcal subgroups in Australia?

B and C

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What factors can affect the likelihood of meningitis colonisation?

Host factors, pathogen factors and exposure.

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What host factors can predispose someone to meningitis?

Genetics

Young age

Recent respiratory infection

Neuroanatomical defects (e.g. head injury)

Immunodeficiencies.

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What pathogen factors increase the chance of meningitis infection?

Polysaccharide capsule

Infecting dose

Competing commensals (colonising flora, probiotics)

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How can exposure play a role in developing meningitis?

Environmental factors such as overcrowding, smoke exposure and season increase the likelihood of exposure.

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What is the pathogenesis of bacterial meningitis?

Colonisation of nasopharangeal mucosa
Invasion of blood stream
Survival and multiplication
Crossing of BBB
Invasion of meninges and CNS
Increased permeability of BBB
Pleocytosis and increased ICP
Release of proinflammatory compounds
Neuronal injury

True or false: the meningitis pathogen causes damage to the body.

False.

It’s not the pathogen that causes damage, rather the body’s response.

What are the clinical features of meningitis in adults?

Common non-specific symptoms/signs:

Fever

Vomiting/nausea

Headache

More specific symptoms:

Stiff neck

Altered mental state

Photophobia

Seizures

What are the clinical features of meningitis in children?

Non-specific symptoms/signs:

Fever

Vomiting/Nausea

Irritable/unsettled

Refusing food/drink

More specific symptoms:

Altered mental state

Bulging fontanelle

Why is meningitis more difficult to diagnose in infants/children?

Because they present in a very non-specific way.

What are the signs of a N. meningitidis (meningococcal) infection?

Meningitis, or Septicaemia (meningococcaemia) – petechial or purpuric (non-blanching) rash Or both together

What is the relationship between meningitis and meningococcaemia?

Meningococcaemia is meningococcus in the blood, meningitis is in the meninges. If you have meningitis, you have at one stage had to have had meningococcaemia because the only way meningococcal can get into the nasopharynx is via the blood.

Which investigations are performed in the diagnosis of meningitis?

Blood: FBE, ESR, blood culture and PCR. CSF: pressure, biochemistry (protein, glucose), microscopy (white cells, red cells, Gram stain), culture, PCR. Skin scraping: microscopy (G stain), culture, PCR. Neuroimaging: CT, MRI, PET

Which are the only investigations specific to meningitis?

Culture PCR (viruses - enterovirus, HSV, bacteria - meningo, pneumo. 16s rDNA.) Skin scraping (microscopy - G-stain, culture, PCR)

How is meningitis defined clinically?

By having abnormal CSF.

What doesn't having abnormal CSF tell you?

If it's bacterial or viral meningitis

What are the normal values for CSF in adults?

Pressure: 60% blood (\>2.5mmol/L)

What are the CSF values for viral meningitis?

Pressure: normal Appearance: clear White cell count: 100s Red cell count: 0 Gram stain: negative Protein: 60% blood

What are the CSF values for bacterial meningitis?

Pressure: raised Appearance: cloudy White cell count: 1000s Red cell count: 0 Gram stain: positive Protein: \>1g/L Glucose: \<40% blood

What are the CSF values for bacterial meningitis?

Pressure: raised Appearance: cloudy White cell count: 100s Red cell count: 0 Gram stain: ZN positive Protein: \>1-5g/L Glucose: \<30% blood

What are the contraindications for lumbar puncture?

Signs suggesting raised ICP Shock Extensive or spreading prura After convulsions until stabilised Coagulation abnormalities Local superficial infection Respiratory insufficiency

What concentration of lymphocytes results in a "cloudy" macroscopic appearance of the CSF?

200-500 x 10⁶/L cells

What concentration of lymphocytes results in a "turbid" macroscopic appearance of the CSF?

500-1000 x 10⁶/L cells

What concentration of lymphocytes results in a "bloody" macroscopic appearance of the CSF?

5,000-6,000 x 10⁶/L cells

True or false: there is no overlap between CSF protein vs. the number of white cells for bacterial, viral or TB meningitis?

False - there's heaps.

True or false: It's possible to distinguish from the initial CSF whether someone has bacterial or viral meningitis.

False. It is impossible to distinguish from the initial CSF whether someone has bacterial or viral meningitis.

What is the effect of antibiotics on CSF values?

Higher glucose, lower protein. No change in cell count.

What are the 4 stages of treatment for meningitis?

Resuscitation/Life support Fluids (SIADH  moderate restriction) Antibiotics Steroids Contact prophylaxis for others.

Which antibiotics are used to treat infants, children and adults for bacterial meningitis?

Intravenous 3^rd generation cephalosporin (e.g. cefotaxime/ceftriaxone)

Which antibiotics are used to treat neonates/infants \<3 months of age for bacterial meningitis?

Intravenous 3rd generation cephalosporin (e.g. cefotaxime/ceftriaxone) + IV penicillin and gentamicin

What is the most common sequela for meningitis?

Hearing loss

Why are the sequelae for meningitis so variable?

Because it depends on which part of the brain is damaged.

What effect did steroids have on the reducing sequelae for Mallawian children with meningitis?

No effect.

What effect did steroids have on the reducing sequelae for adults?

Reduced sequelae.

What is the difference between encephalitis and meningitis?

Encephalitis is inflammation of the brain due to direct invasion of grey matter. It's almost always viral (HSV) and results in an altered conscious state, including confusion, disorientation, altered behaviour or personality, etc.