Microbiology and Immunology Flashcards
What is meningitis?
Inflammation of the meninges
What is encephalitis?
Inflammation of the brain parenchyma
What is myelitis?
Inflammation of the spinal cord.
What is neuritis?
Inflammation of the neurons/nerves.
How many die a year from meningitis?
125,000
Which group of people suffer the most deaths from meningitis per year?
Infants and young children
Where is meningitis most prevalent?
In less developed countries - 96%.
What are the two major classifications of meningitis?
Bacterial and aseptic.
What are the two different divisions of bacterial meningitis?
Culture positive and culture negative
Which form of meningitis is the most serious but the second most common?
Bacterial meningitis
What are the 3 different types of aseptic (culture negative) meningitis?
Viruses, non-infectious and other (e.g. TB, fungal, etc.)
What is the most common cause of meningitis?
Aseptic meningitis (culture negative)
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.
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
What are the most common meningococcal subgroups globally?
A, C, W-135 and X
What are the most common meningococcal subgroups in Australia?
B and C
What factors can affect the likelihood of meningitis colonisation?
Host factors, pathogen factors and exposure.
What host factors can predispose someone to meningitis?
Genetics
Young age
Recent respiratory infection
Neuroanatomical defects (e.g. head injury)
Immunodeficiencies.
What pathogen factors increase the chance of meningitis infection?
Polysaccharide capsule
Infecting dose
Competing commensals (colonising flora, probiotics)
How can exposure play a role in developing meningitis?
Environmental factors such as overcrowding, smoke exposure and season increase the likelihood of exposure.
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 3rd 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.
