What is Meningitis

Meningitis is an inflammation of the membranes covering the brain and spinal cord, called the meninges. It is caused when germs infect the cerebrospinal fluid (CSF), which circulates around the brain and spinal cord. The infection can be caused by three kinds of germs; bacteria, viruses and fungi.

Viral meningitis is the most common and less severe type.  Almost all patients recover without any permanent damage, although full recovery may take many weeks or months. Bacteria however, cause severe infections which can lead to permanent damage or death. Fungi also cause severe infections but are much less frequent than bacterial meningitis

Septicaemia is caused when bacteria enter and then multiply rapidly in the bloodstream, this manifestation of the infection may be seen alone or in addition to meningitis.

Bacteria causing meningitis

Most cases of bacterial meningitis are caused by one of the following bacteria:

• Neisseria meningitidis (meningococcus);
• Streptococcus pneumoniae (pneumococcus);
• Haemophilus influenzae type b (Hib);
• Eschericia coli (E. Coli), seen mainly in newborn babies;
• Streptococcus agalactiae B, (Group B Strep or GBS) seen mainly in newborn babies;
• Listeria monocytogenes, seen mainly in newborn babies or persons with impaired immunity;
• Mycobacteria tuberculosis (Tuberculosis or TB), seen in countries where tuberculosis is prevalent

The first three bacteria on the list (meningococcus, pneumococcus, and Hib) are by far the most frequent causes of meningitis world-wide.

The meningococcus can be subdivided into distinct groups called serogroups, of which serogroups A, B, C, Y and W135 are responsible for over 95% of cases meningitis and septicaemia. Although 6 distinct groups, called types, of Haemophilus influenzae have been identified, type b causes almost all human illness. There are almost 90 distinct groups , called serotypes, of the pneumococcus. In children less than five years of age, up to 13 of these serotypes cause most serious illnesses. In older children and adults a much larger number of pneumococcal serotypes cause disease – 23 cause around 85% of serious illnesses.

Transmission of the disease

Meningitis germs share the same method of transmission from person to person. The first step occurs when the bacteria land on the mucosa of the back of the nose and throat. The bacteria colonise the surface of the mucosa, usually without causing any symptoms. This is called the carrier state, because the bacteria may persist in the nose and throat for weeks or months. The meningitis bacteria do not survive very long outside of the body. Infection spreads from person to person by direct contact with secretions from the nose and throat which contain the bacteria. Spread from a carrier to another person requires close, direct physical contact, combined with activities such as kissing, coughing, and sneezing which result in production of large numbers of droplets which can be contaminated with bacteria.

The carrier state is very common but meningitis bacteria cause disease only in susceptible persons. Although many people are carriers, the bacteria cross the mucosa of the nose and throat and invade the blood stream in only a small proportion, around %1, causing the signs and symptoms of meningitis or septicaemia to develop. Once in the blood, they multiply and produce toxic materials. If the bacteria reach a certain critical concentration in the blood, they are able to cross through the walls of the tiny blood vessels, or capillaries, in the meninges.  The bacterial toxins and the excessive responses of the body to the infection cause inflammation of the meninges resulting in the symptoms and signs of meningitis.

Groups at risk

The peak age groups at risk of bacterial meningitis are infants of six to 18 months of age. About 50% of cases of meningococcal disease occur in children under the age of five years and there is a second disease peak in adolescents 15-19 years of age.

With the decline of immune function in the elderly as the result of aging and the increase in disease affecting the immune system, the incidence of diseases caused by meningitis bacteria increases in this group.

Those people with disease or conditions which affect the immune system are also at increased risk.