7 Bacterial Meningitides Flashcards by Hannah Frank

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

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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%

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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)

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Chronic meningitis is characterized by symptom progression or persistence for …

≥ 4 weeks

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What organism currently accounts for over half of all bacterial meningitis cases?

Streptococcus pneumoniae

Starting to see abx-resistant strep too - boo hiss

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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

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Community acquired meningitis is usually caused by what three organisms?

S pneumoniae
H influenzae
N meningitidis

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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

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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

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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)

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Classic triad of meningitis symptoms

Fever

Headache

Neck stiffness

Other presenting Sx include:
Nausea/vomiting
Sleepiness
Confusion
Irritability 
Delirium

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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

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Additional tests to consider (other than blood tests) for meningitis

Cultures (blood, nasopharynx, urine, skin lesions, respiratory secretions)

Lumbar puncture and CSF analysis

Neuroimaging

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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)

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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

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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)

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Predominant agents of neonatal meningitis

Streptococcus agalactiae

Escherichia coli

Listeria monocytogenes

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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