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					Chapter 35 –
Infections of the
Central Nervous
System
MLAB 2434 – Clinical Microbiology
Keri Brophy-Martinez
General Concepts

   Infections of the CNS are of critical
    concern and positive laboratory
    findings are “critical values”
   Infections may be caused by bacteria,
    fungi, viruses or parasites
Anatomy of CNS

   Brain, Spinal Cord and Cranial Nerves
   Meninges
       Dura mater
       Pia arachnoid
       Pia mater
   Subarachnoid space between pia
    arachnoid and pia mater; CSF
   Page 981 Figure 35-1
CSF

 Unique body fluid produced by
  filtration and secretion from
  specialized capillary tufts of the
  four ventricles of the brain
 Circulates around brain and spinal
  cord under pressure
 Serves as cushion for brain and
  spinal cord
CSF Characteristics

   CSF is a clear and colorless sterile fluid
       Adults
         • Protein 15-45 mg/dL
         • Glucose 40-80 mg/dL
         • WBC 0-7
       Newborns
         • Higher levels of protein & glucose
   Infections indicated by increased cell
    counts and alterations in protein and
    glucose
CNS Infections

   Portals of entry for bacteria
     Respiratory (most common route of
      community-acquired infections)
     Auditory
     Bloodstream
     Neural routes
     Contiguous sites
Types of CNS Infections

   Meningitis
       Also called “leptomeningitis”
       Inflammation around blood vessels within
        the subarachnoid space
   Encephalitis/ Meningoencephalitis
       Diffuse inflammation of the cerebral
        cortex
       Observe mental changes or neurologic
        signs
       Common in viral infections
Types of CNS Infections
(cont’d)
   “Aseptic Meningitis”
     CSF shows predominance of
      lymphocytes with no organisms on
      direct examination
     Many cases are NOT aseptic, but
      due to viruses, fungi, parasites or
      some bacteria
Types of CNS Infections
(cont’d)
   Brain Abscesses
       Areas of tissue destruction containing
        organisms and inflammatory cells
       Occur as spread from other body sites or
        trauma to skull; infecting organism
        depends on predisposing conditions
       Non-traumatic abscesses mostly are
        aerobic and anaerobic streptococci
Bacterial CNS Infections

   Acute Bacterial Meningitis
     Limited to the pia mater and pia
      arachnoid layers
     Symptoms include photophobia,
      headache, nausea, vomiting, and
      stiff neck or Brundzinski sign
     In infants, only symptoms may be
      irritability, poor feeding, and
      restlessness
Bacterial CNS Infections
(cont’d)
   Acute Bacterial Meningitis (cont’d)
       Infants
         •   Group B Strep
         •   L. monocytogenes
         •   H. influenzae
         •   S. pneumoniae
         •   E. coli
       Children
         • N. meningitidis
         • S. pneumoniae
         • H. influenzae
Bacterial CNS Infections
(cont’d)
   Acute Bacterial Meningitis (cont’d)
       Adolescents
         • N. meningitidis
         • S. pneumoniae
       Adults
         • N. meningitidis
         • S. pneumoniae
       Elderly
         • Gram-negative bacilli
         • N. meningitidis
         • S. pneumoniae
Bacterial CNS Infections
(cont’d)
   Acute Bacterial Meningitis (cont’d)
       Lab findings
         • Leukocytosis with left shift and toxic
           changes, such as toxic granulation &
           Dohle bodies
         • Increased CSF protein
         • Decreased CSF glucose
       Increased intracranial pressure
        (may cause neurologic changes in
        adults and retardation in children)
Bacterial CNS Infections
(cont’d)
   Mycobacterial Infection
     Most commonly M. tuberculosis
       Enters by respiratory route and spread via
        bloodstream
       CSF cells are mostly lymphocytes and
        monocytes
       Mycobacteria are few and CSF should be
        centrifuged to concentrate before
        culturing/gram staining
Bacterial CNS Infections
(cont’d)
   Spirochetal Infections
     Lyme Disease
     Neurosyphilis
   Viral Infections – common agents
    listed on page 984
   Parasitic Infections – common agents
    listed on page 987
   Fungal Infections-common agents
    listed on page 986
Laboratory Diagnosis of
CNS Infections
   CSF Collection
       Lumbar puncture in lower back
       3 to 4 tubes collected
         •   1st = chemistries
         •   2nd = microbiology
         •   3rd = cell counts
         •   4th = special procedures (if collected)
       Process ASAP
Laboratory Diagnosis of
CNS Infections (cont’d)
   CSF Analysis
      Acute Bacterial Meningitis
         •   CSF turbid or cloudy
         •   WBC increased with predominance of neutrophils
         •   Increased CSF protein
         •   Decreased CSF glucose
       Centrifugation concentrates organisms
       Should be plated on at least BAP, CA and broth;
        MAC if Gram-negative bacilli are expected
       Bacterial Antigen Testing
         • Current literature indicates routine bacterial antigen
           testing is of limited value
Laboratory Diagnosis of
CNS Infections (cont’d)
   CSF Analysis
       Viral Meningitis
         • Number of lymphocytes increased
         • Diagnosis based on PCR or EIA


       Fungal Meningitis
         • Gram stain or India ink
         • Culture held for 4-6 weeks
Laboratory Diagnosis of
CNS Infections (cont’d)
   CSF Analysis
       Tuberculous meningitis
         •   Increase in lymphocytes
         •   Increase in protein
         •   Decrease in glucose
         •   AFB stain & culture
         •   PCR can be used; however, false
             positives common
                        Characteristic Findings in
                        Meningitis
                  Bacterial     Fungal        Tuberculous   Viral         Syphilitic    Parasitic




Organisms seen    See notes     See notes     See notes     None          None          See notes
in CSF




Cell count        100-100,000   Normal- 500   50-500        Normal-200    100-750       Normal-200
(leukocytes/mL)   Neutrophils   Lymphocytes   Lymphocytes   Lymphocytes   Lymphocytes   Lymphocytes/
                  predominate   predominate   predominate   predominate   predominate   Eosinophils
                                                                                        predominate

Protein (mg/dL)   100-500       Normal- 250   Normal- 150   Frequently    50- 250       Usually increased
                                                            normal




Glucose (mg/dL)   <30           Normal-       <45           Normal        Normal        Normal- decreased
                                decreased

				
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