Microbiology - CNS infections Flashcards
How does pyogenic meningitis appear macroscopically?
Shows a thick layer of suppurative exudate covering the leptomeninges over the surface of the brain
How does pyogenic meningitis appear microscopically?
There are neutrophils in the subarachnoid space
What are some of the causative organisms of community acquired bacterial meningitis?
Pneumococcus, meningococcus, Haemophilus influenzae, listeria (if >60y/o)
How is bacterial meningitis treated?
IV ceftriaxone 2g BD (or chloramphenicol if allergic) + IV dexamethasone 10mg QDS for 10 days
If listeria cover is required how is bacterial meningitis treated?
IV Amoxicillin/ampicillin 2g 4 hourly (or co-trimoxazole if allergic)
If penicillin resistant pneumococci cover is required how is bacterial meningitis treated?
IV Vancomycin or IV/PO rifampicin
What is the most common cause of viral meningitis?
Enteroviruses e.g. ECHO virus
How is viral meningitis diagnosed?
viral stool culture, throat swab and CSF PCR
How is viral meningitis treated?
Generally supportive as self-limiting
How is viral encephalitis treated?
14 days IV aciclovir or 21 days if immunocompromised
What are some of the clinical features of encephalitis?
Insidious onset, meningismus, stupor, seizures, confusion, psychosis, speech and memory problems
How is encephalitis diagnosed?
LP, EEG, MRI
What are some of the clinical features of meningitis?
Fever, rash, severe headache, neck stiffness, photophobia, vomiting, drowsiness, confusion, severe muscle pain, convulsions
What bacterial meningitis causing organisms are neonates most susceptible to?
Listeria, group B strep, E.coli
What bacterial meningitis causing organisms are children most susceptible to?
Haemophilus influenzae
What bacterial meningitis causing organisms are adolescents most susceptible to?
Neisseria meningitidis
What bacterial meningitis causing organisms are adults most susceptible to?
Strep. pneumoniae, neisseria meningitidis
What bacterial meningitis causing organisms are elderly people most susceptible to?
Strep. pneumoniae, listeria
What bacterial meningitis causing organisms are people with head trauma or post-neurosurgery most susceptible to?
Staph aureus, staph epidermidis, aerobic gram negative bacilli
What bacterial meningitis causing organisms are immunocompromised people most susceptible to?
Strep pneumoniae, neisseria meningitidis, listeria, aerobic GNB
What bacterial meningitis causing organisms are people with a basilar skull fracture most susceptible to?
Strep pneumoniae, H.influenzae, GABHS
Which cranial nerves are most susceptible to exudate as a complication of bacterial meningitis?
CNs III, VI
What are the 3 methods of pathogenesis of bacterial meningitis?
- Nasopharyngeal colonisation
- Direct extension of bacteria e.g. mastoiditis
- From remote foci of infection e.g. pneumonia
How does tuberculous meningitis occur and who is most at risk?
Due to reactivation of TB
Most common in elderly
How is tuberculous meningitis treated?
Isoniazid and rifampicin (+pyrazidamole, ethambutol)
What are the features of cryptococcal meningitis?
Fungal
Mainly in HIV patients
CD4<100
Aseptic picture on CSF
How is cryptococcal meningitis treated?
IV amphotericin B/ flucytosine
Fluconazole
What type of organism is Haemophilus influenzae?
Gram negative rods/coccobacilli
What percentage of bacterial meningitides are culture negative?
10-15%
What are the distinguishing features of viral meningitis on CSF?
10-1000 lymphocytes predominantly, everything else is usually normal, except the protein can be slightly raised
What are the distinguishing features of bacterial meningitis on CSF?
10-10,000 polymorphs (neutrophils) predominantly, positive gram stain, high protein and <70% of blood glucose
What are the distinguishing features of tuberculous meningitis on CSF?
10-1000 lymphocytes predominantly, +/- gram stain, high or very high protein and <60% of blood glucose
What is aseptic meningitis?
Non-pyogenic bacterial meningitis
CSF - low WCC, slightly raised protein, normal glucose
Much bigger differential than viral meningitis
What are some of the treatable causes of aseptic meningitis?
HSV 1 + 2, syphilis, listeria, TB, carcinomatous, sarcoidosis, vasculitis, migraine
Who should undergo a CT scan prior to LP?
Immunocompromised patients, history of CNS disease, new onset seizure, papilloedema, abnormal level of consciousness, focal neurological deficit
Should antibiotics be given before or after a LP?
Immediately after a LP but if the LP will be delayed >30mins then give IV antibiotics first
How should people who have been in contact with meningitis be prophylactically treated?
600mg PO rifampicin 12 hourly for 4 doses OR
500mg PO cirprofloxacin as a single dose OR
250mg IM ceftriaxone as a single dose (125mg IV for children)
What should people given rifampicin be warned of?
Reduced efficacy of oral contraceptives, red colouration of urine and staining of contact lenses
What vaccines are available for meningitis?
Neisseria meningitis, H. influenzae and strep pneumoniae
