Flashcards in Exam #7: Bacterial Infections of the CNS Deck (74):
What are the two categories that CNS infections are divided into?
Meningitis= infections of the meninges
Encephalitis= infections of the brain parenchyma itself
What must microbes disrupt to gain access to the CNS?
What is hematogenous spread?
Spread through the bloodstream e.g. bacteremia
What are the different modes of entry to the CNS?
1) Hematogenous spread
2) Spread from an adjacent site
3) Direct inoculation (rare)
4) Neuronal spread e.g. HSV
What is acute pyogenic meningitis?
Bacterial meningitis that leads to the proliferation of neutrophils
What is aseptic meningitis?
Viral meningitis (historical term, meningeal inflammation without growth on culture)
How does bacterial meningitis compare to viral meningitis?
Bacterial is generally more severe
Who is predisposed to get meningitis?
- Pneumonia & chronic OM
- 10-20 % population are carriers
- History of recent UTI-->easier to get into the CNS
- MAC (terminal) Complement deficiencies
- Outbreaks are most common in winter
Generally, individuals with altered or underdeveloped immune status are at an increased risk of developing bacterial meningitis
What are the common virulence factors associated with bacterial pathogens that cause CNS infections?
- Capsules= anti-phagocytic
- Fimbriae, pilli, & outer membrane= function in attachment & colonization
Describe the general pathophysiology of meningitis.
1) Bacterial penetration of the BBB
2) Inflammatory reaction*
- Many of the clinical manifestations are a result of the immune response in the confined area of the brain
3) Cell wall & toxin components of bacteria exacerbate the inflammatory response
- IL-1 & TNF-a -->ICP, Altered cerebral blood flow, Cerebral edema
What symptoms are characteristic of meningitis?
Stiff neck (nuchal rigidity)
What CSF abnormalities are associated with bacterial meningitis?
*Presence of PMNs
What CSF abnormalities are associated with viral meningitis & encephalitis?
Normal or slight increased protein & pressure
What is the approach to empirical treatment of suspected CNS infection?
1) Empirical abx therapy is generally initiated
2) Age, predisposing factors, and other symptoms may provide clues
3) Examination of CSF & results should direct treatment plan
Who is most commonly infected with bacterial meningitis?
Infants & children
What are the MOST common etiological agents that cause bacterial meningitis in children?
Listen in order:
Group B step.
What is the most common cause of bacterial meningitis in neonates (<1 month)?
Group B Strep (S. agalacticae)
Note that this is especially common in kids that are less than 2 months old
What pathogen becomes increasingly prevalent in the teenage years?
What pathogen becomes more prevalent in the very young & old?
List the characteristics of S. pneumoniae.
Gram positive coccus
What is the most common cause of vaccine preventable death in the US?
What clinical syndromes may pneumococcal meningitis follow?
List the virulence factors associated with S. pneumoniae.
Pneumolysin= kills WBC
Describe the course of pneumococcal meningitis infection.
How is pneumococcal meningitis diagnosed?
- Gram stain CSF
- Latex agglutination
- Standard culture....etc.
How is pneumococcal meningitis treated?
*Medical emergency, begin empirical abx therapy with vancomycin & a cephalosporin*
How is pneumococcal meningitis prevented?
Vaccination; however, note that there are 90 different capsular polysaccharides
- Not ALL are covered
- However, currently we have a varieties of polysaccharide vaccines
What is PPV23 & what is the problem with PPV23?
This is the 23 valent vaccine for S. pneumonia that came out in the 1980s--DOESN'T work well in young kids
What are the current vaccine recommendations for S. pneumoniae
- Recommended for kids >2 with chronic illness, immunosuppression, & other risk factors
- Also recommended for adults >65
What is PCV13?
Pneumococcal polysaccharide conjugated nontoxic diptheria toxin
- 13 serotypes
List the characteristics of Neisseria meningitidis.
Gram - diplococcus
Kidney bean appearance
How does LOS differ from LPS?
- Shorter side chains
- No repeating polysaccharide
How is Neisseria meningitis cultured?
What infections does Neisseria meningitis cause?
How is Neisseria meningitis transmitted?
What are the clinical features of Neisseria meningitis infection? How does meningcococcal meningitis differ from pneumococcal meningitis?
Neisseria meningitis presents as:
- Abrupt onset fever
- Neck pain
i.e. as typical meningitis
However, meningococcal meningitits also is accompanied by:
- multi-organ failure
What causes the rash seen in Neisseria meningitis infection?
How is Neisseria meningitis treated?
Vancomycin and/or a cephalosporin followed by once N. meningitidis is identified PCN
How is meningococcal meningitis prevented?
Serotypes A, C, Y, W-135, BUT NOT B
What serotype causes half of the meningococcal meningitis causes in children under 2? Is there a vaccine for this strain?
- Serotype B
How is meningococcal meningitis diagnosed?
- Recognize clinical signs & symptoms
- Gram stain CSF
- Rapid antigen detection in CSF
Describe the current meningococcal vaccine that is used in clinical practice.
"MCV4" -Meningococcal Conjugate Vaccine
Tetravalent polysaccharide conjugate vaccine
List the characteristics of Streptococcus agalactiae.
Gram + cocci
What patient population is most susceptible to GBS meningitis?
What other infections are caused by GBS?
Soft tissue infections
Why is the neonate susceptible to GBS infection?
- 10-30% of pregnant women are colonized by GBS
- Thus, maternal intrapartum GBS colonization is a MAJOR risk factor for the development of early onset disease in infants
*Note that maternal colonization increases risk of infection x25
What virulence factors are associated with GBS?
Aside from maternal GBS colonization, what else increases the risk of GBS meningitis in the neonate?
- Obstetric issue
- GBS bacteuria
- Previous infant with GBS infection
- African American
- Low GBS antibody
What are the characteristics of early onset GBS disease?
Early onset= within the first week of life
Disease is characterized by bacteremia, pneumonia, & meningitis
- Respiratory distress
- Labored breathing
*Note that 1/4 that survive will suffer from permanent neurological sequela
What are the characteristics of late onset GBS disease?
Late onset= between 1-3 weeks after birth
Similar signs and symptoms of "early onset," but meningitis is more common
How is GBS diagnosed in the neonate?
- Recognition of clinical signs and the identification of the organisms--FEVER in NEONATE is a BIG DEAL
- Identification of organism in CSF
- Serologic confirmation by presence of Group B antigen
How is GBS treated?
How is neonatal GBS prevented?
- Universal screening of all pregnant women
- Intrapartum antibiotics i.e. high doses of IV PCN ~4 hours prior to delivery
*Note that there is no vaccine to prevent GBS
List the characteristics of Haemophilus influenzae type B.
Gram negative rod
Requires X & V
What serotype of Haemophilus influenzae causes meningitis?
Is there a vaccine for HiB?
Yes, (conjugated) vaccine against the poly-ribitol phosphate (PRP) capsule
What diseases are caused by non-encapsulated Haemophilus influenzae?
What diseases are caused by encapsulated Haemophilus influenzae?
What is the major neurological sequelae from HiB meningitis?
How is HiB diagnosed?
Gram stain CSF
Latex agglutination test
How is HiB treated?
Similar to other forms of bacterial meningitis--broad to narrow spectrum
List the characteristics of Clostridium tetani.
- Gram + rod
- Spore forming--soil & feces
Describe the typical entrance mechanism of Clostridium tetani.
- Spores enter through wound contamination or traumatic inoculation
- Umbilical stump can be contaminated in neonatal tetanus
What is tetanospasmin? Describe the mechanism of action.
- AB tetanus toxin
- B binds to motor neurons via polysaialoganglioside receptors
- Entire toxin is internalized & retrogradely transported to the spinal cord
- In the spinal cord, it activates the release of GABA
- Leads to "SPASTIC PARALYSIS"
What are the symptoms of tetanus?
Descending pattern of symptoms as follows:
How is Tetanus diagnosed?
Mostly based on clinical presentation & exposure history
How is Tetanus treated?
Passive & active immunization
- Administer Ig
- Vaccinate with inactivated tetanus toxin
How is Tetanus prevented?
Vaccination with tetanus toxoid--the "T' in DTaP
*formalin inactivated tetanus toxin*
List the characteristics of Clostridium botulinum.
Gram positive rod
What is Infant Botulism?
"Floppy baby" Sydrome
- Infants ingest honey containing spores & produce toxin
- Most common cause of Botulism in the US
List the characteristics of Listeria monocytogenes.
Gram + rod
What is Listeria monocytogenes associated with?
Consumption of contaminated food i.e. deli meat, milk, cheese, poultry
*Transplacental transmission to neonate
How does Mycobacterium tuberculosis compare to other bacterial meningitis infections? What diseases can it cause?
Chronic symptom onset
- Brain abscess