Meningitis is an infection of the meninges that are membranes that cover the brain and the spinal cord.
What are meninges?
Meninges are 3 connective tissue layers. They consist of the pia mater (closest to the central nervous system organs), the arachnoid and the dura mater (farthest from the brain and spinal cord).
They also include blood vessels and contain cerebrospinal fluid. These are the structures involved in meningitis, an inflammation of the meninges, which, if severe, may become encephalitis, an inflammation of the brain.
What is meningitis?
Meningitis is an infection of the meninges. The infection may be caused by bacteria or a virus, and it leads to the meninges becoming inflamed (swollen). This can cause serious damage to the nerves, brain and the spinal cord.
Symptoms of meningitis
Meningitis is commonly manifested by:
- severe headache
- high fever
- stiffness of the neck
- sensitivity and eye pain on exposure to light
- skin rash
Symptoms can differ in young children and babies.
Types of meningitis
Meningitis may be caused by bacteria and viruses and both types have some distinctive features. Meningococcal disease is the leading infectious cause of death in early childhood.
Bacterial meningitis is very serious and should be treated as a medical emergency. Left untreated this may lead to severe brain damage and infect the blood causing septicimeia. The most common infecting bacteria are Neisseria meningitidis bacteria.
In 2008 and 2009 in England and Wales saw 1,166 cases of meningitis due to this bacteria. However, with the successful vaccination against this bacteria also known as meningococcal bacteria the number of cases have declined. However, there is currently no vaccine to prevent meningococcal group B disease, which is the most common cause of bacterial meningitis in the UK.
Bacterial meningitis is most common in children who are under five years old and is often life threatening in infants under the age of one. It is also common among teenagers aged 15 to 19 years. Of all the cases around 15% are bacterial meningitis and 25% may manifest with septicaemia. In 60% of cases both may present together.
Viral meningitis is the more common but less severe type of meningitis. The number of cases are difficult to estimate since the symptoms are akin to a bout of flu. Viral meningitis is most common in children and is more widespread during the summer months.
Who gets meningitis?
Meningitis may affect people of all age groups. Infants and young children and the elderly are however more at risk. Viral meningitis is the most common cause of the condition. Every year around 2,500 cases of bacterial meningitis, and nearly 5,000 cases of viral meningitis, occur in the UK.
The people most at risk of getting meningitis include:
- those who have CSF shunts placed in their brain for another pathology
- those with defects in the dura
- use of spinal procedures (eg spinal anaesthetics)
- those with bacterial endocarditis
- alcoholism and liver cirrhosis
- intravenous drug abuse
- renal insufficiency
- cystic fibrosis
- sickle cell disease etc.
Crowding (e.g. schools, day care, military recruits and college students) raises risk of meningitis.
Prognosis or outcome
Viral meningitis usually gets better within a couple of weeks but bacterial meningitis needs aggressive treatment.
Bacterial meningitis needs to be treated with antibiotics, admission to the hospital and even admission to the intensive care units.
Meningococcal disease (the combination of meningitis and septicaemia) causes death in around one in 10 cases. In spite of cure some children may go on to develop complications, such as hearing loss, after having bacterial meningitis. Prevention is by complete vaccinations against the infection.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)