CNS Infection/Bacterial Meningitis Flashcards
- Describe the pathogenesis of acute bacterial meningitis.
Organisms first attach to the nasopharynx and evade phagocytosis (colonize), next may be invasion of another site and if penetration of epithelial barrier can lead to blood stream contamination; after bacteremia, bacteria may cause endothelial cell injury and enter the CSF via the choroid plexus
i. Injury of the choroid plexus lead to increase in vascular permeability (vasogenic edema) and vascular thrombosis
ii. Bacterial replication in meninges results in inflammatory response- cytotoxic and interstitial edema
iii. Cerebral infarction is associated with increased intracranial pressure (decreased blood flow) and ischemia; end result is hypoxia and acidosis
What is the major virulence factor and principle immunogen of bacteria that cause meningitis?
Capsular polysaccharide: major virulence factor and principle immunogen; evades phagocytosis by preventing antibody independent opsonization and antibodies form to specific capsular antigen
- Explain how N. meningitides infection causes shock and disseminated intravascular coagulation.
Blocks IgA 1 protease, allowing it to survive on mucosa of the respiratory tract
GNC in pairs that contains LPS in cell wall, Lipid A can activate complement, producing IL-1 and TNF resulting in clinical manifestation of shock and disseminated intravascular coagulation
Associated with septic shock, petechial rash and hemorrhagic destruction of adrenal glands (Waterhouse-Friderichsen syndrome)
- Identify the major etiologic causes of acute bacterial meningitis according to the following age group: Neonates
S. agalactiae (group B, B-hemolytic, GPC), E. coli (GNR) or Listeria monocytogenes
- Identify the major etiologic causes of acute bacterial meningitis according to the following age group: Children
S. pneumonia, Neisseria meningitides, and Haemophilus influenza type b
- Identify the major etiologic causes of acute bacterial meningitis according to the following age group: Adults
N. meningitides, S. pneumoniae
- Identify the major etiologic causes of acute bacterial meningitis according to the following age group: Elderly.
S. pneumonia, Listerial monocytogenes, N. meningitides, H. flu (gram negative cocobacilli) type B and GNR
What is the natural resevoir for bacterial meningitis? What general syndromes are associated with infection?
human reservoir, transmitted person to person via respiratory droplets (3ft. radius rule of thumb); colonize the human nasopharynx
i. Tend to infect: leptomeninges, lungs, middle ear, paranasal sinuses and epiglottis
- Describe the signs and symptoms of acute bacterial meningitis.
a. Aseptic meningitis: CSF is consistent with inflammatory process but bacterial cultures are negative (can be infectious or non-infectious)
b. Septic meningitis= acute bacterial meningitis
i. Symptoms: severe headache, fever, meningismus, altered sensorium, vomiting, seizures, rarely focal findings and pailledema
ii. Sign: Kernig’s (supine, extension of lower leg with upper leg flexed causes pain in hamstrings) or Brudzinski’s sign (supine, attempt to flex the neck without while holding thorax still, will cause involuntary flexion of the hips)
How might one differentiate between aseptic meningitis and acute bacterial meningitis?
i. Glucose: low for septic, often normal for aseptic
ii. Protein: high in septic, mildly elevated for aspetic
iii. Cell count/differential: most elevated in septic, with PMNs predominating, lymphocytes are more associated with aseptic
iv. Gram stain and culture can be used to definitively denote cause
- Describe the principles of treatment of acute bacterial meningitis.
a. Act promptly: do not delay in performing lumbar puncture or rapidly initiating antibiotic therapy
b. Lumbar puncture should be performed on anyone suspected of having acute bacterial meningitis (CRITICAL), should be obtained if possible before the administration of antibiotics
i. Procedure avoided if there is concern the patient has a significant increase in intracranial pressure; brain herniation through the foramen magnum is possible
What are drug and supportive therapies that are used in acute bacterial meningitis?
c. Drug therapy must be bactericidal that penetrate into the CNS; Ceftriaxone, vancomycin/ampicillin (resistant strains of S. pneumonia/ listeria risk), and dexamethasone to reduce inflammatory swelling prior to antibiotics (in those >1mo)
d. Supportive care often includes intubation, fluid restriction (Except in shock, then fluid resuscitation with pressor), mannitol to pull edema out of CNS and seizure precautions
- Discuss strategies that can be used to prevent infections caused by S. pneumonia, H. influenza type b, and N. meningitides.
a. Vaccines available for S. pneumonia (polysaccharide vaccines 23 and conjugate 13), H. influenza type b (Conjugate vaccine) and N. meningitides type b; protein conjugate meningococcal vaccine to prevent serogroup A and C epidemics in high density housing
b. Contact prophylaxis: with cipro, rifampin or ceftriaxone; children in contact with invasive H. flu cases usually given rifampin
- Identify the Gram stain and major patient risk groups for Listeria monocytogenes.
Non-branching gram positive, grow well in refrigerator and has characteristic tumbling motility found in natural environments (water, soil and decaying vegetation) commonly found in raw veggies, raw milk and cheese and meats
At risk groups: elderly pregnant women, and persons with decreased cell mediated immunity (transplant patients i.e.)
What is the pathogenesis of Listeria monocytogenes?
Can enter the body by endocytosis of endothelial cells in small intestine and can enter the blood stream, has a predilection for CNS and placenta
Major virulence factor: evades intracellular killing by action of listeriolysin O and host resistance is correlated with cellular immunity
other illnesses: febrile gastroenteritis: often precedes development of CNS symptoms; includes fever watery diarrhea, nausea, headache, myalgia, and arthralgia
