CNS infections - cellular pathogens Flashcards
In which age group do CNS infections most commonly occur?
0-4 years
Paediatric disease
In which age group do CNS infection have the highest mortality rate?
>65 years
What are the major categories of causes of meningitis?
Viral
Bacterial
Other (eg. TB)
Non infectious
What is the most common casue of meningitis?
Viral
Usually enterovirus
Even though viral meningitis is more common than bacterial meningitis, why is bacterial meningitis more worrying?
Viral meningitis does not cause sequelae, whereas bacterial meningitis does
Bacterial meningitis is more harmful, viral is self-limiting
What is aspetic meningitis?
Any form of meningitis that is not caused by bacteria
Which three bacteria are the commonest causes of meningitis?
H.influenza
N.meningitidis
S.pneumoniae
Which of the bacterial causes of meningitis is the biggest killer?
In Africa, H.influenza A
Why are H.influenza, N. meningitidis and S.pneumoniae the commonest causes of bacterial meningitis?
These bacteria are best at evading the immune system
Encapsulated with polysaccharide capsule > evade phagocytosis and complement activation
At less than three months of age, which additional causes of meningitis are infants susceptible to?
Those acquired in the birth canal
Group B strep, Listeria and E.coli
Describe the host and bug factors that determine the likelihoods of infection?
Describe how pathogens are able to penetrate defences and cause CNS infection?
What are the major clinical features of meningitis?
Non-specific: fever, vomiting/nausea, headache, irritable and stop feeding (children)
More specific: stiff neck, altered mental state, bulging fontanelle, photophobia, seizures
What are the major signs and symptoms of bacterial meningitis?
Fever
Vomiting
Stiff neck
Photophobia
Difficult to wake
Confused
Non-blanching rash
Seizures
What are the signs and symptoms of meningococcal septicaemia?
Non-blanching rash plus:
Fever
Vomiting
Lethargy
Muscle ache/joint apin
Cold extremities
Leg pain
Pale/mottled skin
Breathlessness
Confusion
Difficult to wake
Which investigations are usually carried out to diagnose meningitis?
CSF
Skin scraping
?Blood
?Neuroimaging
Why don’t blood samples provide a definitive diagnosis for meningitis?
May be changes in blood present that are not specific to meningitis
What are the normal values for CSF?
Why can CSF values be unreliable whej diagnosing menigitis?
CSF values differ with age, and meningitis is predominately a paediatric disease
Describe the CSF values for viral, bacterial and tuberculous meningitis?
Describe viral, bacterial and tuberculous meningitis in terms of protein and white cell count in the CSF?
Viral: normal-high protein, normal-high white cells
Bacterial: high protein, very high white cells
Tuberculous: very high protein, high white cells
What are the major contraindications for a lumbar puncture?
Raised ICP
Shock
Extensive purpura
Unstable convulsions
Coagulation abnormalities
Loacl superficial infection
Respiratory insufficiency
Is CSF that is normal in appearrance necessarily normal?
No
Need large cell change to change appearance of CSF
Why is delay in CSF analysis a problem?
CSF cell count rapidly declines due to cell lysis
Unreliable if not measured immediately
What is the problem in using CSF values to diagnose meningitis?
Some bacterial patients will present like viral patients, and vice versa
What is the treatment for meningitis?
Resuscitation/life support
Fluids
Antibiotics
Steroids
Which antibiotics are used to treat meningitis?
Intravenous 3rd generation cephalosporin
For paediatrics, add those that target the ones from the birth canal
What is the most common complication of bacterial meningitis?
Hearing loss
How is encephalitis treated?
Acyclovir
What is encephalitis?
Inflammation of the brain
What is the most common cause of encephalitis?
Almost always viral: HSV
Describe the conscious state in meningitis vs encephalitis?
Meningitis: normal consciousness
Encephalitis: altered conscious state
Describe how meningitis can be prevented?
Conjugate vaccines
