This document discusses the diagnostic approach for meningitis. It outlines the most common etiological agents which can cause meningitis including bacteria like Neisseria meningitidis, viruses like enteroviruses and herpes viruses, fungi such as Cryptococcus neoformans, and parasites including Entamoeba histolytica. The diagnostic approach involves clinical presentation, laboratory examination of cerebrospinal fluid including analysis of cell count, biochemistry, culture and microscopy, as well as blood tests and molecular methods if initial tests are negative. Lumbar puncture to obtain CSF is the mainstay of diagnosis, allowing for analysis of physical characteristics, biochemical features and cytological examination of the fluid.

1. MENINGITIS:
A Diagnostic approach
::::By : Dr Tulika
MD Microbiology

2. Etiology
• Meningitis refers to the inflammation of
meninges.
• The causative agent may be
bacteria,virus,fungus or protozoal.
• Most common agents are: Neisseria
meningitidis, Streptococcus pneumoniae,
Haemophilus influenzae and Mycobacterium
tuberculosis

4. • VIRAL Causes :
• Enteroviruses- ECHO,Coxsackie,Polio
• Paramyxoviruses- Measles,mumps
• Herpes viruses- Herpes simplex,Varicella
zoster
• Adenoviruses
• Arboviruses- Flavivirus, Buniyavirus

5. • FUNGAL Causes:
• Cryptococcus neoformans
• Candida albicans
• Aspergillus
• Histoplasma capsulatum
• Coccidiodes immitis

6. • PARASITIC Causes:
• Entamoeba histolytica
• Naegleria
• Acanthamoeba
• Toxoplasma gondii

7. DIAGNOSIS
• CLINICAL PRESENTATION :
• Fever,headache,nausea,vomitting, altered
sensorium
• Signs : neck rigidity, Kernigs sign,Brudinsky’s
sign
• Infants and young children may however
present with high or low temperature,
drowsiness or irritability and loss of appetite

8. LABORATORY DIAGNOSIS
• SPECIMEN: CEREBROSPINAL FLUID (CSF)
EXAMINATION IS THE MAINSTAY OF
DIAGNOSIS.
• This is obtained by lumbar puncture under
aseptic conditions
• Collected in three sterile containers- one each
for cell count,biochemical examination and
culture

9. Lumbar puncture

10. CSF Analysis in different types of
meningitis

11. Physical examination
• The fluid will be under high pressure.
• Turbid and whitish in bacterial
meningitis,clear and colourless in other types
• Coagulum : Cobweb coagulum is characteristic
of Tuberculous meningitis, in bacterial also
large coagulum appears.Absent in others.

12. CCCCC

13. BIOCHEMICAL FEATURES
• CSF Protein : Highly increased in bacterial,also
in others
• Sugar : greatly reduced in bacterial,only slight
decrease in tubercular and fungal,normal in
viral
• Chloride : Reduced in pyogenic,tuberculous
and fungal,normal in viral

14. CYTOLOGICAL EXAMINATION
• Normally the cells in CSF are not more than 5
• Mostly lymphocytes
• In pyogenic meningitis,this count is increased
to very high numbers upto 1000 or even
more,mostly neutrophils
• The cell count is increased in other types as
well but not as high and are lymphocytes

15. Microscopy
• Gram staining :Gram negative intracellular
diplococcus ,gives a presumptive diagnosis of
the most common etiology _ Neisseria
meningitidis
• Streptococcus pneumoniae: Gram positive
diplococcus
• Similarly other bacteria can be detected

16. Gram stain of CSF showing Neisseria
meningitidis

17. Gram Stain of CSF showing
Streptococcus pneumoniae

18. • If no organisms detected, bacterial antigens
may be detected by Latex agglutination test
on the CSF or in blood
• ZIEHL - NEELSON staining : is used to detect
Acid fast bacillus in suspected tuberculous
etiology
• If negative, PCR can be performed to detect
Mycobacterium tuberculosis DNA

19. Acid fast bacillus in CSF

20. • In suspected fungal etiology,
• INDIA INK preparation is done to demonstrate
capsule of Cryptococcus neoformans

21. Cyptococcus neoformans in India ink

22. CULTURE
• ENRICHED Media like Blood agar and
Chocolate agar are used as the organisms are
fastidious in their growth requirements.
• BHI Broth : ( a liquid enriched media ) is also
used as the specimen is likely to contain very
small number of bacteria which may not grow
in solid media.After overnight incubation
subculture can be made from liquid broth in
solid culture media

23. Neisseria meningitidis in blood agar

24. Neisseria meningitidis on chocolate
agar

25. Antibiotic sensitivity testing
• If growth is found on culture, an antibiotic
sensitivity test is performed.
• Antiboitic to be used for gram positive and
gram negative :

26. • Serological tests for antibody detection :done
for some viruses
• Microbial antigens in
urine:Immunochromatography ( for S.
pneumoniae ) ,Latex agglutination for
Cryptococcus neoformans antigens
• LIMULUS LYSATE TEST : Extremely sensitive for
detection of Bacterial ENDOTOXIN

27. • BLOOD CULTURE : This is important when
meningococcal infection is suspected
• FUNGAL CULTURE :Sabouroud’s dextrose agar
is used .Two sets of media are inoculated and
incubated at 25 C and 37 C .
• For Cryptococcus, Bird Seed Agar is used
• VIRAL Culture : is done using tissue culture or
egg inoculation

28. SEROLOGY
• LATEX AGGLUTINATION TEST : done for
ANTIGEN DETECTION when microscopy and
culture yield negative results.
• For Neisseria meningitidis,Streptococcus
pneumoniae,Haemophilius influenzae
• In neonates , group B Streptococcus ( S.
agalactiae ) and Listeria monocytogenes

29. MOLECULAR METHODS
• PCR : Detects microbial nucleic acid, done for
suspected M. tuberculosis and viral infections
• May also be done on blood samples ,if CSF
based tests yield negative results