Meningitis and encephalitis

Last Review Date: December 4, 2020

What are they?

Meningitis is inflammation of the membranes that cover the brain and spinal cord meninges. Encephalitis is an inflammation of the brain itself. Meningoencephalitis is an inflammation of both the brain and the meninges.

The condition may be from an infection caused by a bacteria, virus, fungus, or parasite, or may be non-infectious in origin. Meningitis and encephalitis can be acute or chronic, and their severity can range from mild and self-limited to fatal. The associated inflammation and swelling increases pressure on the brain and nerve tissue. This can hinder, or permanently damage, the function of nerves and the brain.

Meningitis and encephalitis can also damage the blood-brain barrier that separates the brain from circulating blood and regulates the distribution of substances between the blood and cerebrospinal fluid (CSF). The blood-brain barrier helps keep large molecules, toxins, and most blood cells away from the brain. With the disruption of this barrier, white and red blood cells, immune system chemicals, toxins, increased amounts of protein, and the germs that cause inflammation may be found in the cerebral spinal fluid (CSF). CSF is a clear watery liquid that normally flows freely around the brain and spinal cord. The flow of CSF may slow or become obstructed with meningitis or encephalitis, which can increase CSF pressure, increase pressure on the brain and spinal cord, and decrease blood flow to the brain.


Most cases of meningitis are due to a bacterial or viral infection. The infection may be primary – starting in the meninges, or secondary – spreading from an infection in another part of the body. Viral meningitis is the most common form of meningitis in Australia. It is usually mild to moderate in severity and self-limited. Viral meningitis is frequently caused by an enterovirus or herpes virus but may also be caused by arboviruses (see Encephalitis above).

Bacterial meningitis is a medical emergency. Cases can arise suddenly, with symptoms worsening within hours to a couple of days. Rapid identification and treatment is crucial. Untreated bacterial meningitis is usually fatal. While this condition can be caused by many different types (species) of bacteria, the most common causes are:

  • Streptococcus pneumoniae – called pneumococcal meningitis. Infants under 2 years old and those with compromised immune systems are at greatest risk for it. A pneumococcal vaccine is now given as part of the routine immunisation programme in Australia. It protects against some forms of pneumococcal meningitis
  • Neisseria meningitidis – called meningococcal meningitis. More commonly seen in college students, infants, children, international travellers, and the immune-compromised. It is the leading cause of bacterial meningitis in children and young adults and is highly contagious. There are 13 known serogroups, designated by letters of the alphabet, of which A, B, C, W135 and Y most commonly cause disease. Since the introduction of a meningococcal vaccine, many cases have been prevented however not all strains are covered by the currently available vaccines. 
  • Haemophilus influenzae type b – once the most common cause of bacterial meningitis, its incidence has decreased because of widespread vaccination of children.
  • Group B streptococcus, Escherichia coli, and Listeria monocytogenes are the most common causes of meningitis in the neonate (babies less six weeks old) and may be passed from the mother to her baby.

Chronic meningitis is meningitis that lasts for more than 4 weeks. It may be caused by bacteria such as Mycobacterium tuberculosis, which causes tuberculosis, by Treponema pallidum, which causes syphilis, and by fungi. Fungal meningitis is most commonly seen in immune-compromised patients, such as those with HIV/AIDS, but may affect anyone. The most common causes are Cryptococcus neoformans and Cryptococcus gattii (cryptococcal meningitis), which are inhaled from the environment. Other uncommon fungal causes include Candida species, Aspergillus species and Histoplasma capsulatum

Amoebic meningitis is rare and is usually lethal. It is caused by the free-living amoeba, Naegleria fowleri, a single-cell parasite, which can be found in warm water lakes and rivers. Eosinophilic meningitis may be caused by a parasitic infection such as Angiostrongylus cantonensis, Gnathosoma species and Baylisacarensis species. Cases have been reported in Australia as a result of eating garden snails and slugs.


Encephalitis is an acute infection of the brain characterised by fever, headache and an altered state of consciousness, with or without seizures. Most cases of encephalitis are viral. They may also be focal (limited to a single location) or generalised (spread throughout the brain).

Viral encephalitis may be caused by a variety of viruses including herpes simplex virus, enteroviruses, parechovirus, the rabies virus (from an animal bite), or arboviruses – those spread primarily by infected mosquitoes.

Humans are not the preferred or primary host of the arboviruses. Most people who are infected have mild to moderate symptoms. Only a very small percentage of people develop encephalitis. Throughout the world, different types of arbovirus-related encephalitis may be seen.

Viral encephalitis may also be seen as a secondary condition that occurs a few weeks after a viral illness.

Bacterial, fungal, and parasitic encephalitis are very rare. Bacterial meningoencephalitis may develop from the bacteria that cause meningitis. Tick-transmitted Lyme disease may cause bacterial encephalitis. Toxoplasma gondii, a parasite associated with cats, can cause parasitic encephalitis in some people with compromised immune systems. Other bacteria, fungi, and parasites can occasionally cause encephalitis

Signs and symptoms

Meningitis and encephalitis may start with flu-like symptoms and intensify over a few hours to a few days. Characteristic signs and symptoms of these two conditions may overlap and can include:

  • Fever
  • Severe persistent headache
  • A stiff neck
  • Sensitivity to light
  • Mental changes
  • Lethargy

Other symptoms may include confusion, nausea, vomiting, a red or purple rash, and seizures. Elderly patients may be lethargic and show few other signs. Patients with compromised immune systems may have atypical symptoms. Infants may be irritable and cry when they are held, vomit, have body stiffness, have seizures, refuse food, and have bulging fontanels (the soft spots on the top of the head). It is important that early signs are reported to your doctor as patients with meningitis can deteriorate rapidly.

Encephalitis symptoms may also include neurological problems – difficulty with hearing or speech, loss of sensation, partial paralysis, seizures, hallucinations, muscle weakness, changes in personality, and coma.

Complications and prognosis

The outcome of those with meningitis and encephalitis depends on the specific cause of the condition, the severity, the patient’s health and immune status, and how quickly the condition is identified and treated. Patients with mild cases may recover fully within a few weeks or may have persistent or permanent complications.

Between 6-25 per cent of newborns and up to 16 per cent of adult patients with bacterial meningitis die, despite rapid administration of appropriate treatment. Up to 28 per cent of those who survive may have neurological sequelae including hydrocephalus, deafness, blindness, periodic seizures, and/or some degree of impaired thinking processes. These complications may occur at any age, but newborns are at the highest risk.


Doctors start by asking about the history of symptoms and performing a physical examination. This examination may occur in the emergency room as symptoms may suddenly appear and rapidly worsen over several hours to a couple of days. The doctor may ask about other recent illnesses, exposure to animals, mosquitoes, or ticks, contact with other people who have become ill, recent travel and recent activities. The doctor will note the presence or absence of signs and symptoms frequently associated with meningitis and encephalitis. Neurological examinations may be performed to assess the status of the patient’s nervous system, assessing coordination, vision, hearing, strength and mental status.

Laboratory tests
Laboratory tests are performed to detect, identify, evaluate, and monitor meningitis and encephalitis. These tests are performed in order to:

  • Distinguish infectious diseases from other conditions with similar symptoms
  • Determine the cause – bacterial, viral, fungal, parasitic, or other as rapidly as possible to start and guide treatment
  • Evaluate the patient’s general state of health, immune system status, current signs and symptoms, and current complications to guide symptom relief and to minimise inflammation and neurological or brain damage
  • Where possible, determine the infection’s source; especially important when the causative agent may be a public health concern

Tests include:
Cerebrospinal fluid (CSF) examination. This is a primary diagnostic tool for encephalitis and meningitis. A CSF examination includes a core group of common tests and a wide variety of other tests that can be ordered and performed on a sample of CSF fluid. CSF is collected using a procedure called a lumbar puncture or spinal tap.

Initial CSF tests - The initial basic set of CSF tests that are often performed with suspected infections of the central nervous system include:

  • Physical characteristics. Normal CSF appears clear and colourless. The appearance of the sample of CSF is usually compared to a sample of water. In infections, the initial pressure of CSF during collection may be increased, and the sample may appear cloudy due to the presence of white blood cells (WBCs) or microorganisms.
  • CSF protein. Only a small amount is normally present in CSF because proteins are large molecules and do not cross the blood/brain barrier easily. Increases in protein are commonly seen with meningitis, brain abscess, and neurosyphilis.
  • CSF glucose. Normal is about 2/3 the concentration of blood glucose. Glucose levels may decrease when cells that are not normally present use up (metabolise) the glucose. These may include bacteria or cells present due to inflammation (WBCs).
  • CSF total cell counts. WBCs may be increased with central nervous system (CNS) infections.
  • CSF WBC differential. Small numbers of lymphocytes, monocytes (and in neonates, neutrophils) are normal in a sample of CSF. There may be:
    • an increase in neutrophils with a bacterial infection
    • an increase in lymphocytes with a viral infection
    • sometimes an increase in eosinophils with a parasitic infection
  • CSF Gram stain for direct observation of bacteria
  • CSF India Ink stain to assess for Cryptococcal meningitis
  • CSF culture and sensitivity for bacteria and fungi, which may take several days to grow

Additional or follow-up CSF tests - If any of the initial tests are abnormal, then additional infectious testing may be ordered. This may include one or more of the following:

  • Detection of viruses by PCR – detection of viral genetic material (DNA, RNA) such as herpes, enteroviruses and parechovirus.
  • Detection of bacteria by PCR- detection of bacterial genetic material for Neisseria meningititis or Streptococcus pneumoniae.
  • CSF Cryptococcal antigen – to detect a specific fungal infection
  • Other CSF antigen or PCR tests – depending on which organism(s) are suspected
  • Specific CSF antibody tests – depending on which organism(s) are suspected

Less commonly ordered CSF infectious diseases tests include:

Several other types of CSF testing may occasionally be ordered to help distinguish between viral and bacterial meningitis:

  • CSF lactic acid - often used to distinguish between viral and bacterial meningitis. The level will usually be increased with bacterial and fungal meningitis while it will remain normal or only slightly elevated with viral meningitis.
  • CSF lactate dehydrogenase (LD) - used to differentiate between bacterial and viral meningitis.

Laboratory tests on samples other than CSF - may be ordered along with or following CSF testing and may include:

  • Blood glucose, protein, FBC (full blood count) – to evaluate and to compare with CSF levels.
  • Blood cultures may be ordered to detect and identify bacteria in the blood.
  • Cultures of other parts of the body may be performed to detect the source of the infection that led to meningitis or encephalitis.
  • Urine antigen test to detect Streptococcus pneumoniae antigen.
  • Tests for antibodies in blood for a variety of viruses. If there is a four-fold rise in the titre of the antibody between two samples collected about a month apart, then it indicates a recent infection by that infectious agent.
  • Urea and electrolytes (U&E), LFTs, CRP – tests that evaluate organ function.
  • Immunological, metabolic, endocrine and toxicology tests to assess for non-infectious causes.

Non-laboratory tests
Imaging tests may be performed to look for signs of brain inflammation or abnormalities but may be unremarkable with encephalitis. Brain damage, tumours, bleeding, and abscesses may be detected. Tests may include:

  • CT (computed tomography)
  • MRI (magnetic resonance imaging)
  • Ultrasound
  • EEG (electroencephalography) – to detect abnormal brain waves


There are vaccines available for Haemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis. Widespread vaccination of children has drastically reduced the incidence of Haemophilus influenzae type b.

Those with close respiratory contact to someone who has meningococcal or Haemophilus influenza type b meningitis may be prescribed antibiotics for a few days to decrease their risk of developing an infection.

Arbovirus risk can be minimised by limiting exposure to mosquitoes, limiting outdoor activities at night, wearing long sleeved clothing, using insect repellents, and eliminating freestanding water around the home. Ensuring appropriate vaccination has occurred prior to overseas travel can also lower risk.


Acute bacterial and fungal meningitis and encephalitis are considered medical emergencies. The goals with treating encephalitis, meningitis, and meningoencephalitis are to target the cause of the inflammation, minimise tissue damage and complications, and relieve patient symptoms. Bed rest in a dark quiet room, fluids, pain relief for head and body ache, anti-inflammatory drugs, anti-seizure medications, sedatives, and anti-nausea agents may be prescribed. Corticosteroids may be given in some cases to help reduce tissue and brain swelling.

Treatment for bacterial causes
Bacterial infections are frequently treated with a broad-spectrum antibiotic as soon as, or even before, the cause is positively identified. This therapy may then need to be modified once culture results or other types of testing identify the specific bacteria and its susceptibility to antimicrobial agents. Antibiotics chosen must be able to pass through the blood-brain barrier and reach sufficient concentration in the CSF. They may be administered intravenously and reach high levels in the blood. Patients are monitored for signs of drug toxicity and for organ function. Depending on the type of bacteria and the state of the patient’s immune system, treatment may need to be continued for weeks, months, or even years.

Medical procedures are sometimes necessary to drain infected abscesses or sinuses. These procedures may need to be repeated.

Treatment for viral causes
Many cases of viral encephalitis and meningitis may be mild to moderate in severity, self-limited, and only require monitoring, rest, and relief of symptoms. Patients with more severe cases may require hospitalisation. For viral encephalitis due to herpes or varicella-zoster viruses, doctors may prescribe an antiviral drug such as aciclovir. For those due to HIV, highly active antiretroviral therapy may be required.

Treatment for fungal causes
Fungal infections are usually treated with intravenous anti-fungal drugs. Treatment may continue for an extended period of time. Patients with a compromised immune system may have to continue oral therapy indefinitely to prevent the infection from recurring.

Treatment for parasitic causes
Acute parasitic meningoencephalitis caused by the amoeba Naegleria fowleri is frequently fatal because there are no antimicrobial agents proven effective to treat this infection. Infections with Toxoplasma, Angiostrongylus and other parasitic agents may resolve with appropriate anti-parasitic drugs.

Common questions

1. Are meningitis and encephalitis always caused by infections?
Very rarely, meningitis and encephalitis may be due to a non-infectious cause. This may include an autoimmune disorder that targets components of the nervous system, a reaction to a drug treatment, or certain cancers.

2. Can other conditions have similar symptoms?
Other serious conditions can cause some of the same symptoms as meningitis and encephalitis but have different causes and treatments. These include a brain abscess, brain lesion, drugs, trauma, or subdural empyema - a collection of pus in the space between the dura mater and arachnoid layers of the meninges.

3. Does meningitis and encephalitis start in the brain?
Meningitis can be caused by an infection in the blood or an infection in close proximity to the brain (ear or sinus infection) that allows the organisms to enter the CSF, or head trauma that allows bacteria in the sinuses to cross the blood-brain barrier. Encephalitis can be caused by infections that originate in the respiratory tract, gastrointestinal tract, or the blood that can spread to the central nervous system.

4. Is meningitis contagious?
It depends on the microorganism that is causing meningitis. People who have been exposed to someone who has meningococcal meningitis may be prescribed antibiotics for a few days to minimise their chance of developing it. There are vaccinations available for Streptococcus pneumoniae, Haemophilus influenzae type b and Neisseria meningitidis that are the most common causes of bacterial meningitis and can be transmitted to others in respiratory secretions.

5. Once I have had meningitis or encephalitis, can I get it again?
It is possible to acquire this type of infection again. Some patients with compromised immune systems must continue their antimicrobial therapy indefinitely to prevent recurrence.

Related pages

On this site
Tests: Cerebrospinal fluid examinationGlucoseTotal proteinFull blood countProtein electrophoresisAntibody identificationAcid fast bacilli cultureBlood culture, Herpes simplex virus 1 & 2Lyme disease serologyRubellaSyphilis
Conditions: Guillain-BarrĂ© syndromeHIVLyme diseaseMultiple sclerosis, Travellers' diseasesTuberculosisWest Nile virus

Elsewhere on the web
Better Health Channel: Meningitis
The Children's Hospital at Westmead: Meningitis

UK sites
Meningitis Research Foundation 
Meningitis helpline

US sites
National Meningitis Association
Journal of the American Medical Association: Meningitis