Meningitis, Acute

Meningitis is defined as inflammation of the leptomeninges, the tissues surrounding the brain and spinal cord. It is marked by an abnormal number of white blood cells in the cerebrospinal fluid (CSF). The focus of this review is on the infectious causes of acute meningitis.

  • Diagnosis
  • Monitoring
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Fever, headache, altered sensorium, and stiff neck

Laboratory Testing

  • CDC meningitis overview
  • Initial testing is nonspecific – CBC, electrolytes
    • Normal WBC does not rule out meningitis
  • Cerebrospinal fluid (CSF) exam – necessary to determine presence of meningitis
    • CSF opening pressure – limited value if normal; usually >300 mm in bacterial but ≤300 in all others
    • Microscopic exam – white count >1,000 cells/µL in >90% of patients with bacterial meningitis
      • Neutrophils (typically >80%) usually predominate in bacterial meningitis
        • Lymphocytes/monocytes predominate in viral and fungal meningitis
          • Early viral disease may have ≥50% neutrophils, but shift toward lymphocytes/monocytes
        • Immunocompromised patients may not demonstrate elevated WBC results in bacterial meningitis
      • Immunocompromised patients and those with Listeria monocytogenes may have normal CSF WBC results
        • Listeria may also present with normal WBC results and high protein CSF
      • Normal WBC result does not exclude bacterial meningitis
    • Protein – usually elevated (>200 mg/dL) in bacterial and fungal meningitis; usually <200 in viral
    • Glucose – usually low (<10mg/dL) in bacterial and tuberculous meningitis; normal to minimally low in viral and fungal meningitis
    • Gram stain – useful if positive
    • Culture
      • Bacterial culture – gold standard for diagnosis of bacterial meningitis
        • Anaerobic culture may be important for post-neurosurgical meningitis or shunt meningitis
      • Fungal and AFB cultures require HIGH VOLUME taps (at least 10cc fluid)
      • Viral culture from CSF not indicated
    • CSF antigen antibody testing, when appropriate (eg, pneumococcal antigen, dimorphic fungi serology, cryptococcal antigen)
  • PCR testing for enterovirus, Epstein-Barr virus, herpes simplex virus, varicella-zoster virus, cytomegalovirus, arboviruses
  • Blood cultures – may be positive in up to 2/3 of patients in Western countries in bacterial meningitis
    • Less sensitive if antibiotics have been administered
  • Other tests to consider
    • Rapid serum HIV antibody and plasma viral load testing – rule out acute HIV infection
      • Use for patients with risk factors and aseptic meningitis
    • RPR – rule out syphilis
    • Urinalysis – may reveal urinary tract infection as etiology of bacteremia
    • Malaria blood film – in areas where malaria is endemic
      • Has a negative predictive value of 98%

Imaging Studies

  • If focal findings are present or patient is significantly immunocompromised, consider CT/MRI prior to CSF tap
  • Chest x-ray – may be useful in diagnosing pneumonia as etiology (usually S. pneumoniae)

Differential Diagnosis

  • Serology should not be used to monitor status of disease


  • Incidence
    • Bacterial – 4-6/100,000
    • Viral – ~10/100,000 in U.S. (Putz, 2014)
  • Occurrence/transmission
    • Hematogenous dissemination (bacteremia, viremia)
    • Trauma – surgery, head trauma (basilar skull fracture, as nidus for development of infection)


Risk Factors

  • Advanced age
  • Male sex
  • Low socioeconomic status
  • Crowded living conditions
  • African American ethnicity
  • Dural defects
  • Intravenous drug abuse
  • Immunosuppression (eg HIV, connective tissue diseases, malignancy)
  • Indwelling shunts
  • Recent neurologic surgery

Clinical Presentation

  • Headache
  • Fever
  • Meningismus, nuchal rigidity, altered sensorium, seizures, photophobia
    • Kernig sign – resistance to passive extension of the knee when the hip is flexed at 90% (highly insensitive, very specific [Putz, 2014])
    • Brudzinski sign – spontaneous flexion of hips and knees on passive flexion of the neck (highly insensitive, very specific [Putz, 2014])
  • Nausea, emesis
  • Focal neurologic deficits, hemiparesis
  • Rash – VZV, meningococcus, Rocky Mountain spotted fever, ehrlichiosis
  • Complications


  • Immediate institution of antimicrobial therapy if bacterial, tuberculosis, or fungal meningitis is suspected
  • For bacterial – cover S. pneumonia, N. meningitidis, H. influenzae
  • For focal neurologic causes – cover HSV until studies rule out HSV


  • Viral – mumps vaccination
  • Bacterial
    • H. influenzae vaccination in childhood
    • S. pneumoniae vaccination in childhood
      • Conjugate vaccine for infants, polysaccharide vaccine for other at-risk groups
    • N. meningitidis vaccination in children 11-18 years (if vaccinated between 11 and 15 years, recommend booster), freshmen entering college, complement-deficient patients, asplenic patients
      • Chemoprophylaxis for close contacts of patients with N. meningitidis
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Electrolyte Panel 0020410
Method: Quantitative Ion-Selective Electrode/Enzymatic

Cerebrospinal Fluid (CSF) Culture and Gram Stain 0060106
Method: Stain/Culture/Identification

Glucose, Plasma or Serum 0020024
Method: Quantitative Enzymatic

Cell Count, CSF 0095018
Method: Cell Count/Differential

Glucose, CSF 0020515
Method: Enzymatic

Protein, Total, CSF 0020514
Method: Reflectance Spectrophotometry

Blood Culture 0060102
Method: Continuous Monitoring Blood Culture/Identification


Limited to the University of Utah Health Sciences Center only

Fungal Culture 0060149
Method: Culture/Identification


Need 5cc fluid to culture for fungus

Viral Meningitis Panel by PCR, Cerebrospinal Fluid 2007063
Method: Qualitative Polymerase Chain Reaction

Viral Meningoencephalitis Panel by PCR, Cerebrospinal Fluid 2007062
Method: Qualitative Polymerase Chain Reaction

Meningitis/Encephalitis Panel by PCR 2013305
Method: Qualitative Polymerase Chain Reaction


A negative result does not exclude a diagnosis of meningitis or encephalitis due to infection

Acid-Fast Bacillus (AFB) Culture and AFB Stain 0060152
Method: Stain/Culture/Identification/Susceptibility

Streptococcus pneumoniae Antigen, CSF 0061162
Method: Qualitative Immunochromatography


False positives may occur because of cross-reactivity with other members of S. mitis group; clinical correlation recommended

Patients who have received the S. pneumoniae vaccines may test positive in the 48 hours following vaccination; avoid testing within 5 days of receiving vaccination 

Samples from patients taking antibiotics >24 hours may show a false-negative result.

Wright Stain

Encephalitis Panel with Reflex to Herpes Simplex Virus Types 1 and 2 Glycoprotein G-Specific Antibodies, IgG, CSF 2008916
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Semi-Quantitative Chemiluminescent Immunoassay

Encephalitis Panel with Reflex to Herpes Simplex Virus Types 1 and 2 Glycoprotein G-Specific Antibodies, IgG, Serum 2008915
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Semi-Quantitative Chemiluminescent Immunoassay

Neisseria meningitidis Tetravalent Antibodies (Serogroups A, C, W-135 and Y), IgG 2001603
Method: Quantitative Multiplex Bead Assay


Not intended for diagnosis of infection or serotyping

Acanthamoeba and Naegleria Culture 0060245
Method: Qualitative Culture/Microscopy

West Nile Virus Antibodies, IgG and IgM by ELISA, CSF 0050228
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Ehrlichia and Anaplasma Species by Real-Time PCR 2007862
Method: Qualitative Polymerase Chain Reaction

Lymphocytic Choriomeningitis (LCM) Virus Antibodies, IgG & IgM, CSF 2001628
Method: Semi-Quantitative Indirect Fluorescent Antibody

Cryptococcus Antigen, CSF 0050195
Method: Semi-Quantitative Enzyme Immunoassay

Blastomyces dermatitidis Antibodies by EIA with Reflex to Immunodiffusion, Serum 3000236
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Qualitative Immunodiffusion

Blastomyces dermatitidis Antibodies by EIA with Reflex to Immunodiffusion, CSF 3000231
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Qualitative Immunodiffusion

Histoplasma Antigen by EIA, Serum 0092522
Method: Semi-quantitative Enzyme Immunoassay


Rarely positive in chronic cases

General References

Bamberger DM. Diagnosis, initial management, and prevention of meningitis. Am Fam Physician. 2010; 82(12): 1491-8. PubMed

Brouwer MC, Tunkel AR, van de Beek D. Epidemiology, diagnosis, and antimicrobial treatment of acute bacterial meningitis. Clin Microbiol Rev. 2010; 23(3): 467-92. PubMed

Kim KS. Acute bacterial meningitis in infants and children. Lancet Infect Dis. 2010; 10(1): 32-42. PubMed

Logan SA, MacMahon E. Viral meningitis. BMJ. 2008; 336(7634): 36-40. PubMed

Mace SE. Acute bacterial meningitis. Emerg Med Clin North Am. 2008; 26(2): 281-317, viii. PubMed

Putz K, Hayani K, Zar FA. Meningitis. Prim Care. 2013; 40(3): 707-26. PubMed

Somand D, Meurer W. Central nervous system infections. Emerg Med Clin North Am. 2009; 27(1): 89-100, ix. PubMed

Srivastava R, Murphy MJ, Jeffery J. Cerebrospinal fluid: the role of biochemical analysis. Br J Hosp Med (Lond). 2008; 69(4): 218-21. PubMed

van de Beek D, de Gans J, Tunkel AR, Wijdicks EF. Community-acquired bacterial meningitis in adults. N Engl J Med. 2006; 354(1): 44-53. PubMed

Ziai WC, Lewin JJ. Update in the diagnosis and management of central nervous system infections. Neurol Clin. 2008; 26(2): 427-68, viii. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Bagdure SR, Fisher MA, Ryan ME, Khasawneh FA. Rhodococcus erythropolis encephalitis in patient receiving rituximab. Emerg Infect Dis. 2012; 18(8): 1377-9. PubMed

Durtschi JD, Erali M, Bromley K, Herrmann MG, Petti CA, Smith RE, Voelkerding KV. Increased sensitivity of bacterial detection in cerebrospinal fluid by fluorescent staining on low-fluorescence membrane filters. J Med Microbiol. 2005; 54(Pt 9): 843-50. PubMed

Hanson KE, Alexander BD, Woods C, Petti C, Reller B. Validation of laboratory screening criteria for herpes simplex virus testing of cerebrospinal fluid. J Clin Microbiol. 2007; 45(3): 721-4. PubMed

Martins TB, Jaskowski TD, Tebo A, Hill HR. Development of a multiplexed fluorescent immunoassay for the quantitation of antibody responses to four Neisseria meningitidis serogroups. J Immunol Methods. 2009; 342(1-2): 98-105. PubMed

Polage CR, Petti CA. Assessment of the utility of viral culture of cerebrospinal fluid. Clin Infect Dis. 2006; 43(12): 1578-9. PubMed

Powers AE, Bender JM, Kumánovics A, Ampofo K, Augustine N, Pavia AT, Hill HR. Coccidioides immitis meningitis in a patient with hyperimmunoglobulin E syndrome due to a novel mutation in signal transducer and activator of transcription. Pediatr Infect Dis J. 2009; 28(7): 664-6. PubMed

Medical Reviewers

Last Update: January 2018