Lecture 19: CNS Infections Flashcards
Meningitis
- Infection/inflammation of the meninges (protective layer), the protective lining that protects the brain and the spinal cord
- 70% of meningitis cases occur in the first 5 years of life
- Bacterial Meningitis: acute, life threatening } occurs early in life -> untreated can be fatal
- Aseptic/viral meningitis - usually self limiting
- Clinical symptoms of meningitis include nuchal rigidity (can’t move your head), headache, confusion, drowsiness
Inflammation of the Meninges
Presses down on brain when inflamed
Encephalitis
Inflammation of brain tissue - most often viral infections
Meningoencephalitis
Inflammation of both the meninges and the brain tissues
Pathophysiology of Meninges
- Seeding of the meninges usually occurs from the bloodstream - secondary to bacteremia or viremia
- Direct inoculation from trauma, neurosurgery or instrumentation
- Lots of neurotropic viruses
- Replicating pathogens that lead to an increase in intracranial pressure (ICP), worsening brain edema and decreasing cerebral blood flow (CBF)
Bacterial Meningitis in Neonates (<1yr old)
- Highest risk for bacterial meningitis due to an immature immune system
- Difficult to diagnose - general sign and symp are often diff to interpret, alertness, feeding/vomiting, fever
- Impact - blindness, hearing loss, development delays and even death
Most common: Streptococcus agalactiae (Group B Strep)
Others to think about: Listeria monocytogenes, Escherichia coli (inhibits gut)
Bacterial Meningitis in Children
Streptococcus pneumoniae (part of normal flora), Haemophilus influenzae (less common), all vaccines that are highly efficacious - so not seen as often as before
- Children carry what makes them sick
- Typically affects un-immunized children, the elderly and/or immunocompromised
Above belt
Gram +’ve
Below belt
Gram -‘ve
Bacterial Meningitis in Adults
- Vaccine preventable - rare
- Most often in the immunocompromised and elderly
- Typically seeds from blood or injury
Most common: Streptococcus pneumoniae, Neisseria meningitidis
Less common: Listeria monocytogenes (bc of immune response decrease, moreso with elderly)
Streptococcus agalactiae - Group B Streptococcus (GBS)
- Vaginal carriage rates ~ 30-40%
- Incidence of about 1 case per 1000 births
- Less than 1% of full-term babies that become carriers of GBS and can develop meningitis (also pneumonia and/or bacteremia)
- Early onset - <7 days post birth - detected via prenatal screens at 35 weeks;
- Late onset 8-30 days
- Antimicrobial helps with early onset, not late
Escherichia coli (E. coli)
- E. coli is the second most common cause of bacterial meningitis in newborns
- E. coli causes between 25-33% of cases of meningitis in newborns, but less than 2% of cases of meningitis at all other ages
- Highest colonizer of the GI tract
- Acquired via the vaginal canal during birth
- Premature and low-birth weight babies are at higher risk of E. coli meningitis than full term newborns
Listeria monocytogenes in infants
- Gram +’ve bacilli
- Environmental sources such as soil, dust, animals, and some foods (soft cheeses, processed meats)
- Most infections occur after oral ingestion, with access to the systemic circulation after intestinal penetration
- Intrauterine infections: Transplacental transmission following maternal bacteremia
- Risk of neonatal disease in vaginally colonized mothers
Listeria monocytogenes Adults: elderly or immunocompromised
- Sporadic cases in adults - about 3 +’ve cases at KGH over last 3 yrs (very low levels acc seen)
- Much more common amongst the immunocompromised and or elderly patients
Haemophilus influenzae (type B)
- Late 1970’s was the most common cause of meningitis
- Highest rate of HiB carriage was in infants 6-18 months of age
- In 1992, the HiB vaccine was introduced
- Vaccine initiated at 2 months
- HiB is now very rare in Canada
- We don’t screen for very rare
Streptococcus pneumoniae
- Most common
- 40% of ppl carry Streptococcus pneumoniae, starting in the 1st yr of life (carriage in nose and throat)
- Sporadic cause of meningitis in children and adults
- Children under 2, and elderly are high risk
- Low rates of pneumococcal meningitis
- Vaccine @ 4 months also given to elderly
- Incidence of S. pneumoniae invasive disease is decreasing as a result
Neisseria Meningitidis
- Carriage in nose and throat of 10-20% of teen and adults
- High rates of colonization common in undergrads in young students, prisons, etc (places w high concentrations of ppl)
- Most common cause of bacterial meningitis
- High risk in under 5
- Sporadic vs. epidemic (schools, colleges, military)
- 250-750 cases of meningococcal disease occur every year in Canada (sporadic outbreaks/cases)
- Antibiotic prophylaxis for “close contacts” of ppl
lab diagnosis of bacterial meningitis (results)
- antibiotics
- bacteria metabolize sugar: so low sugar levels (<40 mg / dL)
- high levels of protein (>250 mg / dL)
- CSF space -> neutrophils (high levels -)
- opening pressure elevated
lab diagnosis of viral meningitis
- antiviral
- can’t metabolize so normal or high glucose levels (40-85 mg / dL)
- No protein (doesn’t produce it)
- CSF space = lymphocytes (high numbers - WBC < 100 x 106 / L)
- opening pressure normal
lab diagnosis of fungal meningitis
- glucose same as bacteria - eat sugar so low levels (<40 / dL)
- moderate to high protein, but not as high as bacteria protein (25-500 mg / dL)
- opening pressure variable
- predominance of lymphocytes
lab diagnosis of bacterial meningitis (what tests)
1 thing you do is blood culture (where is it coming from)
- CSF cell count and differential (stuff from results portion)
- gram stain (morphological ID of the organisms) can be used to help inform antimicrobial choice
- bacterial culture
- PCR for culture negative cases
lab diagnosis of fungal meningitis (what tests)
cryptococcus neoformans (massive capsule); yeast w a large cap
- meningitis / meningoencephalitis
- more common in T cell immunocompromised: lymphoma, AIDS, steroids
- less aggressive infection that bacterial
if not treated high mortality
lab diagnosis for C. neoformans meningitis
- culture (24-48hrs)
- latex agglutination
- if present, neoformans will bind to the latex beads and visible agglutination will occur
description of viral meningitis
- milder than bacterial meningitis w death or permanent brain damage being very rare
- self limiting in majority of cases
- 1/2 of all cases are caused by enteroviruses
enteroviruses
- results in self limiting meningitis most of the time
- asymp or fairly non specific
- most common in summer and late fall
- fecal-oral transmission or direct contact w resp secretions
(poliovirus, echovirus, coxsackie A and B)
poliovirus - FYI
- most asymp
- paralytic poliomyelitis (irreversible) most serious manifestations (asymm flaccid paralysis that affects spinal cord not brain)
- major in developing countries -> lack of vaccine distribution, global polio eradication,
- uses inactivated polio virus
w viral meningitis how accurate is the virus culture
only +’ve in 50% of viral meningitis cases
- PCR for enteroviruses
encephalitis description
- no or mild symptoms
- serious cases: nausea/vomit, headache, fever, confusion, drowsiness
- Urgent symptom is altered level of consciousness
- you need crows, mosquitoes for west nile (no human transmission)
- HSV, enteroviruses, arboviruses
herpes encephalitis
HSV-1 is most important cause of fatal sporadic encephalitis (fatal if not treated)
- brain infection thought to occur by direct neuronal transmission
- factors that precipitate this infection are unknown
arbovirus encephalitis
geo distribution
- west nile**
- eastern equine encephalitis
- western equine encephalitis
- st louis encephalitis
- japanese encephalitis
west nile virus
- seasonal incidence in North America, also in Africa, Middle East, Europe, Russia, India, and Indonesia
- mild sympt, disease can be severe
lab diagnosis of encephalitis
- clinical sympt - 1st screen
- PCR testing
- Antibody detection in serum (serology)
brain abscess etiology
- direct trauma or accident or through hematogenous spread from blood
- direct extension from the sinuses
- tend to be polymicrobial (aerobic and anaerobic bacteria)
- drained surgically, antibiotics do not penetrate absess
