What is bacterial meningitis?
Bacterial meningitis is extremely serious and potentially life-threatening. It can result in brain damage, hearing loss or learning disability, however it is fortunately quite rare.
What causes bacterial meningitis?
There are three common bacteria that most commonly cause meningitis, by spreading from the upper respiratory tract. These are:
• Neisseria meningitidis (in meningococcal meningitis)
• Streptococcus pneumoniae (in pneumococcal meningitis)
• Haemophilus influenzae (in haemophilus meningitis)
Meningococcal meningitis - caused by the bacteria Neisseria meningitidis, this bacteria also causes septicaemia if it invades the bloodstream.
- It is mainly transferred from person to person via coughing or in the saliva of those who carry the bacteria in their throat and nose harmlessly.
- 10-20% of the general population are carriers. During epidemics as many as 95% of healthy people may be carriers of the bacteria, but less than 1% ever get meningitis.
- Recently in the UK there has been a noticeable
increase in the numbers of 15- to 24-year-olds affected. This may suggest an
increased likelihood of outbreaks of meningococcal infection in institutions, e.g.
schools, colleges and universities.
- The death rate for meningococcal meningitis is four times higher in teenagers
than in children under five years old. The overall mortality rate is between six
and 10 per cent.
Pneumococcal meningitis - caused by a bacteria called Streptococcus pneumoniae, which is a major
cause of ear infections, pneumonia, and septicaemia.
- Meningitis often follows
pneumonia or a sinus infection and commonly occurs with septicaemia.
- The infection is most common in those under two and over 60 years of age.
- People who have had their spleen removed (splenectomy) are at increased risk
of developing this form of meningitis.
- Pneumococcal meningitis is the most serious form of acute meningitis and has
a mortality rate of 20 %. The mortality rate
is higher in adults than in children and increases in those who go into a coma
or have pneumonia as well.
- More than one third of survivors will be left
with neurological problems e.g. deafness, fits or weakness.
Haemophilus meningitis - caused by a bacteria called Haemophilus influenzae.
- Haemophilus influenzae meningitis used to be the most common cause of bacterial meningitis in children under five years old.
- Since the introduction of
Haemophilus influenzae type b immunisation in 1992, the frequency of
haemophilus meningitis has fallen by 87 per cent and there are now probably
less than three new cases per million of the population each year.
E. coli meningitis - is the most common form of meningitis occurring in the first
month of life. The infection is more common in babies where there have been
complications during the birth and where the mother has an E. coli infection of
the urinary tract or uterus.
- In more than 50 per cent of cases of E. coli
meningitis, the baby also has septicaemia.
- There may be few signs of meningitis in infants, especially in those that are
born early. If any infant is unusually drowsy, irritable and feverish, E. coli
meningitis may be a possible cause, particularly if no other source of infection
can be identified.
- The mortality rate can be as high as 50 per cent and is
particularly high in pre-term infants.
TB meningitis - is caused by Mycobacterium tuberculosis.
- It is relatively uncommon in the UK, but may be on the increase, especially in
people whose immune systems have become weakened e.g. people with AIDS,
heavy alcohol users and people who have travelled from areas where the
infection is common in the population.
- TB meningitis most commonly affects very young and very old people who are
exposed to the bacteria without being adequately immunised by the BCG