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Bacterial meningitis

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What is Bacterial Meningitis

Meningitis is inflammation of the meninges (membranes) covering the brain and spinal cord. Meningitis may be caused by infection, such as by bacteria or viruses. Non-infectious meningitis is often referred to as “aseptic meningitis“. This article will focus on bacterial meningitis.

Statistics on Bacterial Meningitis

Overall, the annual incidence of bacterial meningitis is approximately 3 cases per 100,000 population. Incidence is affected by such factors as geography, ethnicity, socio-economic status and availability of immunisation against the various infective organisms. Individuals of any age may be affected, but the very young and elderly (> 60 years) are more susceptible.

Risk Factors for Bacterial Meningitis

The most common causes of meningitis are viral infections that usually resolve without treatment. Implicated viruses include:


Bacteria

Bacterial infections of the meninges are usually extremely serious illnesses, and potentially may result in death or brain damage even if treated.

The most common organisms causing bacterial meningitis, accounting for 80% of all bacterial cases, are:

  • Haemophilus influenzae;
  • Streptococcus pneumoniae (pneumococcus);
  • Neisseria meningitidis (meningococcus)

Other bacterial organisms causing meningitis include:

  • L. monocytogenes: Especially in pregnancy, infants under one month of age, adults over 60 years, cancer patients, or the immunosuppresse;
  • Group B streptococci: Infants < 1 month;
  • Escherichia coli: Infants < 1 month;
  • Staphylococcus aureus: In people who have undergone neurosurgery or with a history of head trauma.


Risk factors for bacterial meningitis include:

  • Extremes of age;
  • Pregnancy;
  • Alcoholism;
  • Diabetes mellitus;
  • Splenectomy;
  • Immunodeficiency syndromes;
  • Head trauma with open skull fracture;
  • Neurosurgical procedures.

Meningitis may also be caused by fungi, chemical irritation or drug allergies, and tumours (aseptic meningitis).

Progression of Bacterial Meningitis

The bacteria which cause acute meningitis may spread to the meninges directly from local structures such as the ear and nasal sinuses, or via the blood stream. Bacterial products then cause an inflammatory response in the body. Inflammatory cells (neutrophils) accumulate in the blood vessels and brain spaces. This is what causes the symptoms and complications of meningitis. Blood vessels in the brain may become blocked, resulting in a stroke or seizure. In some cases, the flow of cerebrospinal fluid may be blocked, causing hydrocephalus (excess CSF in the skull) and raised intracranial pressure, both of which can have serious effects.

Distinguishing between acute, subacute, and chronic forms of meningitis may help identify the bacteria or virus causing the problem. Approximately 25% of patients with bacterial meningitis present acutely within 24 hours of onset of symptoms. Other patients with bacterial meningitis and most patients with viral meningitis present with subacute neurologic symptoms developing over 1-7 days. Chronic symptoms lasting longer than 1 week suggest meningitis caused by some viruses as well as tuberculosis, syphilis, fungi (especially cryptococci), and carcinomatous meningitis.

Late complications of meningitis include decreased intellectual function, poor memory, seizures and deafness.

Symptoms of Bacterial Meningitis

The classic symptoms of bacterial meningitis are headache, neck stiffness and fever. Other symptoms may include photophobia (sensitivity to light), nausea and vomiting, rash, confusion, irritability and neck stiffness.

How is Bacterial Meningitis Diagnosed?

  • Lumbar puncture: This samples the cerebrospinal fluid surrounding the brain. Analysis of the fluid may show immune cells, bacteria, or changes in the composition of the fluid which suggest meningitis;
  • Blood cultures;
  • Blood glucose level;
  • A CT or MRI of the head looking for hydrocephalus, abscess or cerebral oedema;
  • Chest and skull x-ray may be appropriate in some cases.

Prognosis of Bacterial Meningitis

Bacterial meningitis is potentially lethal. Depending on the bacteria involved, mortality may be as high as 20%. The early diagnosis and treatment of bacterial meningitis is essential in the prevention of death or permanent nervous system damage. Viral meningitis is usually not serious, and symptoms often disappear within 2 weeks.

How is Bacterial Meningitis Treated?

Bacterial meningitis is an emergency. Prompt intravenous antibiotic treatment of bacterial meningitis is essential. The type of antibiotic prescribed will depend on the type of organisms causing the infection. Antibiotics will be ineffective if the cause is viral.

Treatment of secondary symptoms including brain swelling, shock and convulsions will require other medications. Patients may need to be cared for in an intensive care unit (ICU).

People who qualify as close contacts of a person with meningitis may require antibiotics to prevent them from getting the disease.

Bacterial Meningitis References

  1. Beaman MH, Wesselingh SL. Acute community-acquired meningitis and encephalitis. Med J Aust. 2002;176(8):389-96. Available from: [Abstract | Full text]
  2. Braunwald E, Fauci AS, Kasper DL, et al. Harrison’s Principles of Internal Medicine (16th edition). New York, NY: McGraw-Hill Publishing; 2005. Book
  3. Kumar P, Clark M (eds). Clinical Medicine (6th edition). Edinburgh: WB Saunders Company; 2005. Book
  4. Therapeutic guidelines: Antibiotic (version 12). Melbourne, VIC: Therapeutic Guidelines Limited; 2003. Available from: [URL Link]

Drugs/Products Used in the Treatment of This Disease:

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Dates

Posted On: 11 September, 2003
Modified On: 15 May, 2018
Reviewed On: 18 May, 2007

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