laboratory diagnosis of meningitis
TRANSCRIPT
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LABORATORY DIAGNOSIS OF MENINGITIS
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Definition
Meningitis• Inflammation of the subarachnoid space or
throughout the leptomeninges
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Types of Meningitis
• Purulent meningitis • Acute• Chronic
• Aseptic meningitis-no growth of bacteria in CSF culture
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• Acute Meningitis-Onset of meningeal symptoms over the course of hours to several days
• Chronic Meningitis-Insidious onset
Signs of meningoencephalitis,symptoms for atleast 4 weeks
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Etiology:PURULENT MENINGITIS:
Hemophilus influenzaeStreptococcus pneumoniaeNeisseria meningitidisGroup B StreptococcusListeria monocytogenesEscherichia coliKlebsiella speciesPseudomonas speciesStaphylococcus aureusS. epidermidis
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• Naegleria fowleri (Primary amoebic meninigoencephalitis)• Acanthamoeba species
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Etiology contd…….
• ASEPTIC MENINGITIS:• Viruses:– Enteroviruses (Echovirus, poliovirus, coxackieviruses)– Mumps– Herpes simplex– Varicella-zoster– Measles– Adenovirus– Arbovirus
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Bacteria:Leptospira interrogans serovars
icterohemorrhagiae & canicolaTreponema pallidumMycobacterium tuberculosis
Fungi:Cryptococcus neoformans
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Bacteria causing purulent meningitis related to age
• Premature newborns:– Escherichia coli, Klebsiella spp, Enterobacter spp, Proteus
spp,Listeria monocytogenes• Infants:– S. agalactiae, L. monocytogenes, H. influenzae, S.
pneumoniae• Children:– N. meningitidis, S. pneumoniae, H. influenzae
• Adolescents:– N. meningitidis
• Adults:– S.pneumoniae
• Old age- L.monocytogenes
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Laboratory Diagnosis
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Specimen collection & transport
CSF collected by inserting sterile wide-bore needle into subarachnoid space between L4 & L5 lumbar vertebrae & CSF allowed to drip into dry sterile container.
2 tubes of CSF should be collected ( 1 for culture, 2nd for other investigations)
Volume of CSF collected critical for detection of certain microorganisms (eg: mycobacteria, Fungi).
Minimum of 5-10ml recommended for collection. Processing too little specimen lowers sensitivity.
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Precautions to be taken:
• CSF sample to be delivered immediately to laboratory
• CSF sample never to be refrigerated• If not rapidly processed, CSF to be incubated
at 350C or at room temperature.
• Exception: CSF sample for viral studies may be refrigerated for as long as 23 hours or frozen at -700C if longer delay anticipated.
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Guidelines for interpretation of results following hematologic & chemical analysis of CSF
Clinical setting
Leukocytes/mm3
Predominant cell type
Protein Glucose
Normal 0-5 None 15-50 mg/dl 45-100 mg/dl
Viral infection 2-2000 (mean of 80)
Mononuclear Slightly elevated (50-100 mg/dl) or normal
Normal
Purulent infection
5-20,000 ( mean of 800)
PMN Elevated (>100 mg/dl)
Low (<45 mg/dl)
Tuberculosis & fungi
5-2000 ( mean of 100)
Mononuclear Elevated (>50 mg/dl)
Normal or low
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Microbiological investigations:
• Microscopy• Culture• Antigen detection• Molecular methods• Miscellaneous tests
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MicroscopyStained smear of sediment:
Gram stain (must on all CSF sediments)Acridine orange fluorochrome stain ( for faster
examination)Wet preparation:
To detect motile amoebaPhase contrast microscopy or light microscopy
Acid fast stain:When tubercular meningitis suspectedAFB difficult to detect in CSF
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• India ink preparation:– To detect cryptococcal
meningitis– Presence of capsulated
budding yeast cells
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Culture:Usually done for all CSF samples received.
CSF sample must be cultured as soon as possible.
If delay anticipated, CSF kept at 35-370 C.
Inoculate specimen on chocolate agar, blood agar & incubate in 5% to 10% CO2at 35-370 C upto 72 hours.
Inoculate specimen on MacConkey agar, incubate aerobically at 35-370 C overnight.
Antimicrobial sensitivity tests to be done for positive cultures.
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Culture contd….
• For CSF fungal cultures, inoculate CSF sediment onto Sabouraud dextrose agar & incubate aerobically at 350 C for 4 weeks.
• Suspected TB meningitis-LJ medium Liquid media Automated culture systems
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• Naegleria or Acanthamoeba speciesBacterial overlay on non-nutrient agar used for detection
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Antigen testing:
• Bacterial antigen testing (BAT):– For rapid detection of antigen from CSF.– Useful in previously treated patients & gram stain
negative CSF specimens with abnormal parameters.– Latex agglutination kits to detect bacterial antigen
directly from CSF– Less than 100% sensitivity & specificity.
• Latex agglutination test for cryptococcal antigen. (CALAS-Cryptococcal Latex Agglutination System)
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Bacterial antigen testing
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Molecular methods:
Polymerase chain reaction for:Mycobacterium tuberculosisHerpes simplex virusEnteroviruses(RT-PCR)
Miscellaneous tests:Adenosine deaminase assayCSF lactate determinations
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Points to Remember• Inflammation of meninges• Purulent/Aseptic ; Acute/Chronic• Bacteria,Viruses,Fungi,Parasites• CSF sample collection-Never refrigerate• Biochemical & cytological parameters• Staining of CSF-Gram staining• Culture• Antigen detection• PCR
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