Microbiology 5 - CNS infections and meningitis Flashcards
Which antibiotic should be used first line in meningitis?
Ceftriaxone
Add amoxicillin if they’re over 50 or immunocompromised - suspected listeria
Is listeria meningitis is suspected, what antibiotic therapy should be used?
Ceftriaxone plus amoxicillin
Which pathogen is most likely to be the cause in myelitis?
Poliovirus
What is myelitis?
Inflammation of the spinal cord
Recall the 3 most likely causative organisms in acute meningitis, and the most susceptible demographic of patient to each
N. meningitidis = young
S. pneumoniae = elderly (so vaccine at 65 years)
H. influenzae = those who haven’t had HiB vaccine
What is the most common cause of meningitis in neonates?
Group B strep
(Women who are colonised with Group B strep in the vagina -> abrasions to the baby during delivery -> infection)
Similar thing can occur with E. coli
What is the most likely causative organism in chronic meningitis?
TB
What is the most likely causative organism in aseptic meningitis?
Enteroviruses e.g. Coxsackie virus
Herpes is another common cause
Aseptic meningitis is the most common infection of the CNS
Describe the rash produced by meningococcal meningitis
Non-blanching purpuric rash
What is the most likely viral cause of encephalitis in the UK and worldwide?
UK: HSV
Worldwide: WNV
Recall 3 possible routes of infection that may cause a brain abscess
Direct expansion from
- otitis media
- mastoiditis
- paranasal sinusitis
What is the most common type of spinal vertebral infection?
Pyogenic vertebral osteomyelitis
What is the most common cause of pyogenic vertebral osteomyelitis?
Infective endocarditis - staph/ strep can be ‘flicked off’ the valve
What is the first investigation to do in suspected meningitis?
Blood cultures (remember that the most common route of entry for CNS infection is haematogenous)
Also do a throat swab to see if they are colonised
Finally, do a blood PCR - not affected by empirical antibiotics
Recall the stains used in CSF analysis to look for a) bacteria b) TB and c) fungi
a) gram stain
b) either auramine stain or ziehl-neelsen
c) India ink
If “alpha haemolytic diplococci” are found in CSF, what is the pathogen causing meningitis?
Streptococcus pneumoniae
What is the normal range for CSF protein?
0.15-0.4
What is the appearance of CSF in purulent vs aseptic vs TB meningitis?
Purulent: turbid
Aseptic/ TB: slightly turbid or clear
What type of cell is elevated in the CSF in purulent vs aseptic vs TB meningitis?
Purulent: polymorphs
Aseptic/ TB: lymphocytes
In which type of meningitis will gram stain antigen tests be positive?
Purulent meningitis
Which type of meningitis produces the most protein in CSF?
TB meningitis
What is the empirical therapy for meningitis?
Ceftriaxone 2g IV bd
Add amoxicillin if >50 or immunocompromised
What are the 4 modes of entry for CNS infection?
Haematogenous spread - most common (many people’s nasopharynx are colonised with Strep pneumoniae or N. meningitidis)
Direct implantation e.g. trauma or neurosurgery complication
Local extension - secondary to established infections e.g. ear infections
PNS into CNS - viruses (e.g. rabies moving from PNS to CNS to cause encephalitis)
What do neurotoxins affect?
CNS and PNS
What class of meningitis is bacterial meningitis usually?
Acute meningitis (especially with Strep. pneumoniae, N. meningitidis and Haemophilus)
Why is it important to ascertain whether it’s meningitis on its own or meningococcal septicaemia?
In septicaemia, there will be depletion of platelets and clotting factors -> this will affect whether you can do an LP or not
What is the mortality and morbidity of acute meningitis?
Mortality = 10% Morbidity = 5-20%
Who is more susceptible to listeria meningitis or encephalitis?
IMMUNOCOMPROMISED individuals eating blue cheese or mayo etc
CSF will contain gram positive cuboidal rods
Which infectious cause of encephalitis can be transmitted from cats to immunocompromised individuals?
Toxoplasma gondii
What is the best scan for looking at parenchymal abnormalities such as abscesses or infarctions?
MRI (superior to CT)
What is the most common cause of meningitis in uncontrolled HIV?
Cryptococcus neoformans -> causes a high pressure meningitis
What is the generic therapy for meningoencephalitis?
Acyclovir + ceftriaxone
Add amoxicillin if over 50 or immunocompromised - suspected listeria
