7 Bacterial Meningitides Flashcards
What are the two broad categories of CNS infection?
Meningitis - inflammation resulting from an infection within the subarachnoid space
Encephalitis - inflammation in the parenchyma
Both can lead to access formation
Toxicity can be systemic due to exotoxin activity
What was the most common cause of bacterial meningitis prior to 1995?
Haemophilus influenzae
Responsible for nearly all of cases
Thanks, vaccine! It’s now down to ~2%
Acute meningitis is characterized by …
Symptom onset of hours to several days
Etiologic agents include members from all major groups of infectious agents (bacteria, fungi, parasites)
Chronic meningitis is characterized by symptom progression or persistence for …
≥ 4 weeks
What organism currently accounts for over half of all bacterial meningitis cases?
Streptococcus pneumoniae
Starting to see abx-resistant strep too - boo hiss
What two things have caused a significant decline in the number of cases of meningitis?
Vaccination (Hib)
Universal screening of pregnant women for Group B Strep
Community acquired meningitis is usually caused by what three organisms?
S pneumoniae
H influenzae
N meningitidis
Hospital acquired meningitis is usually the result of…
Iatrogenic procedures (clinician based, ie Foley catheter, dental surgery) or patients with altered immune status
Gram negative rods
S aureus
Other strep and staph strains
Pathogenesis of bacterial meningitis
Mucosal colonization —> entry to bloodstream —> penetration of BBB —> release of inflammatory cytokines —> WBC diapedesis into the CSF —> increased permeability of BBB —> exudation of serum
Symptoms: edema, increased intracranial pressure, altered blood flow
3 pathways for gaining access to the CNS
Invasion of the bloodstream and seeding of the CNS (most common)
Retrograde neuronal pathway (as with Naegleria)
Direct contiguous spread (from infections, congenital malformations, trauma)
Classic triad of meningitis symptoms
Fever
Headache
Neck stiffness
Other presenting Sx include: Nausea/vomiting Sleepiness Confusion Irritability Delirium
Useful blood studies to consider in meningitis patients
CBC
Serum electrolytes
Serum glucose (compared to CSF glucose) - will be normal in serum but low in CSF
Liver profile
Additional tests to consider (other than blood tests) for meningitis
Cultures (blood, nasopharynx, urine, skin lesions, respiratory secretions)
Lumbar puncture and CSF analysis
Neuroimaging
How do we treat meningitis?
Prompt initiation of appropriate empiric therapy (rational therapy after ID of organism and abx susceptibility testing)
Steroid (usually dexamethasone) to decrease swelling
Intrathecal abx for hospital acquired infections (b/c more aggressive)
Predisposing factors for neonatal meningitis
Neonatal factors:
Immaturity of host defense mechanisms
Immaturity of organ systems
Low birth weight
Maternal factors: Premature rupture of membranes Urogenital infection during late term Intrauterine infection during early term Invasion of the uterine space
SSx of meningitis in neonates
Bulging fontanelle
High pitched cry
Hypotonia
Paradoxic irritability (quiet when stationary, crying when held)
Hyperthermia** (sometimes hypo)
CNS manifestations (lethargy, irritability, seizures)
GI disturbance (anorexia, vomiting, distention, diarrhea)
Respiratory abnormalities (dyspnea, apnea, cyanosis)
Predominant agents of neonatal meningitis
Streptococcus agalactiae
Escherichia coli
Listeria monocytogenes
CDC recommendations for the prevention of neonatal meningitis
Universal prenatal screening for vaginal or rectal colonization with group B strep for all pregnant women at 35-37 weeks gestation
Routine abx prophylaxis for culture-positive women (unless undergoing planned cesarean delivery AND who have not begun labor or had rupture of membranes)
What is the prognosis for neonatal meningitis?
Generally poor (mortality rates of 10-60%)
Survivors typically have permanent defects (ie neuro sequelae)
Most common cause of neonatal bacterial meningitis
Streptococcus agalactiae (aka Group B Strep)
Not to be confused with Strep pneumo - most common cause of ALL bacterial meningitis
Infections of Streptococcus agalactiae in adults is strong linked with…
Underlying immunodeficiences
What does Strep agalactiae look like?
Gram positive coccus
Gray-white colonies with a narrow zone of ß-hemolysis
~80% of cases are transmitted during delivery
Remainder of cases are acquired postpartum
What are the virulence factors for Streptococcus agalactiae?
Fewer compared to Strep pneumo
Capsular polysaccharide
Hyaluronidase and Collagenase (both help it embed deeper into tissue)
Hemolysin
Describe early onset Group B Strep infection
Maternal obstetric complications are common
Symptoms develop during first 5 days of life - but has a better prognosis than late onset disease
Major clinical manifestations are bacteremia, PNA, and meningitis
Describe late onset Group B Strep infections
Maternal obstetric complications uncommon
Symptoms develop from 7 days to 3 months of age (makes Dx more problematic)
Major clinical manifestations are bone/joint infections, bacteremia with concomitant/fulminant meningitis
Poor prognosis
What is this stupid CAMP factor test?
Developed by Christie, Atkins, and Munch-Peterson
Accentuation of hemolysis due to interaction with staph ß-lysin
Only Strep agalactiae will make this pattern
Horrible test but always on boards 🙄
How is Streptococcus agalactiae diagnosed?
Organism isolated form normally sterile areas (ie CSF) as well as from areas with mixed flora
CAMP factor
Other presumptive tests:
ID of group CHO is insensitive
DNA probe is available
Definitive Dx requires isolation from blood, CSF
Gram-negative enteric bacillus that can be a causative agent for neonatal meningitis
E. coli
Encapsulated (K1) strains are associated with meningitis
Source is rectal colonization of mother’s vagina (not an endogenous infection)
Meningitis infections rare in adults but can follow neurosurgical trauma
Predisposing conditions for pneumococcal meningitis
Multiple myeloma
Sickle cell disease
Cardiorespiratory disease
Congenital defects
Non-motile, gram-negative coccobacillus that can potentially cause bacterial meningitis
Haemophilus influenzae
Prior URI and associated or preceding otitis media are common
Usual pattern:
Several days of mild antecedent infection followed by deterioration, SSx of meningitis
Most causative agents of bacterial meningitis occur during the winter, except …
Listeria monocytogenes (occurs in summer)
Describe Listeria monocytogenes
Gram positive motile coccobacillus
Requires reduced oxygen tension for in vitro growth
Non-fastidious and grows at wide range of temperatures (but does require some CO2)
Numerous serotypes exist but only 3 account for most cases
Facultative intracellular pathogen
• In epithelial cells
• In macrophages and monocytes (shuts down phagocytosis)
What are the virulence factors for Listeria monocytogenes
LPS-like surface component
• Antiphagocytic
• Presumably responsible for induction of complement-dependent hemolytic antibodies
Listeriolysin O
• Disrupts the phagolysosome membrane
• Inhibits antigen processing
• Induces apoptosis
The two main manifestations of listeriosis:
Sepsis
Meningitis
Clinical manifestations of neonatal listeriosis
Acquired in uterine results in stillbirth, abortion, death, or PNA, seizures, skin lesions w/ high mortality if undiagnosed early
Acquired form mom’s genital tract —> meningitis
Clinical manifestations of adult listeriosis
Leading cause of meningitis in CANCER and RENAL TRANSPLANT patients
Brain stem encephalitis is a classic feature
How is listeriosis diagnosed
Gram stain of appropriate clinical material
• 60% of meningitis cases are negative
• Organisms are pleomorphic
• Usually grown on blood agar plates
Culture from appropriate clinical material
• Homogenization is required for tissues
“Tumbling” motility in a hanging drop preparation is indicative of …
Listeriosis
Treatment for listeriosis
DOC: IV Ampicillin
Alternate: TMP-SMX
Describe Neisseria meningitidis
Fastidious, gram negative, kidney bean shaped diplococcus
Encapsulated, but only a few serotypes are responsible for disease
The most important (disease causing) serotypes of Neisseria meningitidis
A, B*, C, Y, W135
All but B are part of the quadrivalent vaccine (B has its own vaccine)
Widespread eruption of a rash with petechiae and pink macules within hours is a hallmark sign of …
Meningococcal meningitis (from Neisseria meningitidis)
DIC and gram-negative shock can also occur
Can use the “Tumbler test” to determine if it’s the right rash
How do you diagnosis meningococcal meningitis?
Characteristic petechiae lesions that don’t blanch with pressure
Gram stain CSF
Cultivation of blood on Chocolate agar or Thayer-Martin agar
Detection of capsular polysaccharide in CSF
What is the drug of choice for meningococcal meningitis?
Penicillin G
Chloramphenicol or 3rd gen cephalosporins are alternatives
Chemoprophylaxis of exposed contacts with various drugs
