Microbiology Flashcards
What is meningitis
Inflammation of the meninges
all layers
What can an untreated CNS infection lead to
Brain herniation - death
Cord compression and necrosis - leads to paralysis
Location of a brain infection determines the symptoms - true or false
TRUE
Depends where in the brain is affected and what it is responsible for
What is encephalitis
Infection of the whole brain
How does pyogenic meningitis appear
Pus forming - get a thick suppurative layer on the brain
Would see lots of neuropils microscopically and in LP
What are the classifications of meningitis
Acute pyogenic - bacterial
Acute aseptic - viral
Acute focal suppurative infection - abscess or empyema
Chronic bacterial infection 0 TB
What is the treatment for bacterial meningitis
Ceftriaxone IV
Must give steroids with the antibiotics - dexamethasone
For the over 60s or the immunocompromised you must add in amoxicillin to cover for listeria
What is the most common organism that causes bacterial meningitis
Strep pneumo
Listeria also common in the elderly or immunocompromised
If a patient with meningitis has recently travelled to a country with high penicillin resistance, what should be included in their treatment
Vancomycin
How do you diagnose viral meningitis
Viral stool culture
Throat swab
CSF PCR
How do you treat viral meningitis
Treat symptomatically – anti-emetic, rehydration etc
Usually self limiting so treat supportively
What are the clinical features of encephalitis
Confusion, change in mental state May have neck stiffness or other 'meningitis' symptoms Stupor or coma Seizures Partial paralysis Speech and memory symptosm
Encephalitis has a fast onset - true or false
False
Usually insidious - takes a few days to a week
What investigations would you do for encephalitis
LP
EEG
Blood cultures
CT/MRI -will see changes
What viral cause of encephalitis must you rule out before treating with antibiotics
Herpes simplex
Do you get MRI changes in meningitis
NO
You do with encephalitis - differentiates between them
What are the common signs and symptoms of bacterial meningitis
Fever Cold peripheries Vomiting Drowsiness and lethargy Confusion and irritability Non- blanching rash Severe muscle pain and headache Stiff neck Photophobia Convulsions and seizures
What are the risk factors for bacterial meningitis
Immunosuppression - listeria risk
Neurosurgery or head trauma - staph risk
Fracture of the cribriform plate - strep pneumo
Which organism is the most common cause of bacterial meningitis in neonates
Listeria
This is why pregnant ladies shouldn’t eat certain cheeses etc
Also strep pneumo
Which organism is the most common cause of bacterial meningitis in children
Haem influenza
Which organism is the most common cause of bacterial meningitis in teenagers and young adults
Neisseria meningitidis
Which organism is the most common cause of bacterial meningitis in adults
Strep pneumoniae
Which organism is the most common cause of bacterial meningitis in the elderly
Strep pneumoniae and listeria
What are some of the lifelong consequences of a meningitis
Limb loss Deafness Mental impairment Blindness Cerebral palsy
These will affect around 25% of those who survive meningitis
Which cranial nerves are vulnerable to damage in meningitis
III and VI
If pus collects around them they can be damaged
Describe the pathogenesis of bacterial meningitis
The bugs can come from nasopharyngeal colonization
They can travel from sinusitis, mastoiditis or across skull fracture to reach the brain
Remote focal infections can also track up to the brain - pneumonia etc
Which bacteria can cause meningitis in the immunocompromised population
The typical agents - strep and staph - can still affect
Listeria
TB
Cryptococcus is seen in HIV with a low CD4+
What treatment is required for Cryptococcus meningitis
Seen in HIV patients
Give IV Amphotericin B/Flucytosine and fluconazole
Creates a very high pressure in CSF so must do regular daily LPs to relieve pressure
Where is Neisseria meningitides usually found
Found in the throats of healthy carriers
How does neisseira meningitides reach the brain
Probably gain access to the meninges through the bloodstream.
The bacteria may be found in leukocytes in CSF
What causes the effect in meningococcal meningitis
The endotoxin released by Neisseria meningitides
Where is H influenza usually found
It is part of normal throat microbiota
What does H influenza need in order to grow
Blood factors
Therefore need to be cultured on chocolate agar
Where is strep pneumoniae usually found
The nasopharynx
Who is most susceptible to strep pneumonia meningitis
Hospitalized patients, patients with CSF skull fractures, diabetics/ alcoholics and young children
May be linked to CNS implants like cochlear
Some occur secondary to pneumonia
Which group will struggle to fight off encapsulated organisms
Those without a spleen
Puts them at higher risk
The pneumococcal vaccine also protects against meningitis - true or false
True
What antibiotic is needed to treat listeria
IV ampicillin or amoxicillin
What type of bacteria is listeria
Gram positive bacilli
What are the signs of TB meningitis
Usually a reactivation of the infection in the elderly
Will have been non-specifically ill for weeks
May have had previous Tb in CXR
How do you treat TB meningitis
Isoniazid and rifampicin are the key ones
Also add pyrazinamide and ethambutol
What investigations would you do for suspected meningitis
Bloods - cultures, FBC, U&E< LF, PCR, serology
Throat swab - culture
LP - unless signs of sepsis
Can move onto viral PCR if that is the likely cause
What tests can be done on a CSF sample in suspected meningitis
Haematology - cell count and differential
Microbiology - gram stain (done immediately) and cultures (takes several days)
Chemistry - glucose and protein
How will glucose change in the CSF of someone with meningitis
It will be lower than usual
This is because the bacteria present will consume glucose
All bacterial meningitis will gave a positive culture - true or false
FALSE
around 10-15% are culture negative
Also even short duration of treatment can turn samples negative (e.g. if LP was delayed but antibiotics were started)
Which viruses commonly cause meningitis
Enterovirus - in autumn/summer and associated with GI symptoms
HSV1 and 2 - will have cold sores
In immunocompromised can be EBV or CMV
Describe the CSF findings in a viral meningitis
Predominantly lymphocytes
Negative gram stain
Normal protein (may be slight increase)
Normal glucose
Describe the CSF findings in a bacterial meningitis
Predominantly polymorphs
Positive gram stain
High protein
Lower glucose - less than 70% of BG
Describe the CSF findings in a tuberculosis meningitis
Predominantly polymorphs
Positive or negative gram stain
Very high protein
Lower glucose - less than 60% of BG
What is aseptic meningitis
Means a non-pyogenic bacterial meningitis - doesn’t produce pus
Will have normal glucose and protein and less WBC
What are the indications for hospital admission in suspected menigitis
Signs of meningeal irritation An impaired conscious level
A petechial rash
Febrile or unwell and have had a recent fit
Any illness, especially headache in those who have come into close contacts with meningococcal infection
What is the immediate management of suspected meningitis on admission
Take blood for culture and coagulation screen
Start empirical treatment
Take throat swab
Disrupt and swab any skin lesions
When should you do a CT before an LP
Immunocompromised History of CNS disease New onset seizure Papilloedema - or other signs of raised ICP Abnormal level of consciousness Focal neurological deficit
What are the indications for LP
ALL adults with suspected meningitis require one
UNLESS there is a clear contraindication or there’s a confident clinical diagnosis
Antibiotics should be started immediately, before investigations have come back (e.g. LP) - true or false
In suspected meningitis it is TRUE
Why are steroids given in meningitis
It reduced unfavourable outcomes and mortality
Give alongside the doses of antibiotics
When would you not give steroids in meningitis
Post-surgical meningitis, severe immunocompromise, meningococcal or septic shock or those hypersensitive to steroids
How can you prevent secondary cases of meningitis
Report all clinically suspected cases to public health ASAP
GPs can contact close contacts to allow implementation of prophylaxis
Label those at risk as higher risk persists for 6 months
What prophylaxis is available for those who have been in contact with
600mg rifampicin every 12 hours for 4 doses
Lower dose for young kids - 10mg/kg
OR
500mg ciprofloxacin single dose in adults
What vaccines are available for meningitis
Neisseria meningitidis - groups A,C,W,Y
H. influenza - HiB
Strep pneumo - pneumococcal vaccine
What is a normal protein ratio in CSF
<0.4
What is a normal glucose ratio in CSF
> 0.6 glucose (CSF:blood),
Usually around 60-70% of blood glucose
What are the normal CSF white and red cell counts
No red cells and no more than 5 white cells per mm3
What does normal CSF look like
Clear and colourless with no blood or neutrophils
What is meant by a blanching rash
Disappears when pressure is applied
Is it safe to do an LP in a patient without a CT first
Nope
Need to look for signs of raised ICP, focal deficits or seizure
If CT is abnormal or symptoms present then not safe due to herniation risk
How do Neisseria meningitidis appear on staining
Gram-negative diplococci
What prophylaxis is given to those who come into contact with meningitis
Ciprofloxacin
How can you treat HSV encephalitis
IV aciclovir
How do you treat encephalitis
IV Ceftriaxone and dexamethasone
Amoxicillin for listeria cover
Acyclovir if HSV risk
Middle ear infections can lead to encephalitis - true or false
True
Recurrent infections increase risk as it can spread to brain
Which organisms can cause brain abscesses
- strep pneumoniae
- Bacteroides
- staph
