Many of the meningococci seem to be harmless and may prevent more dangerous meningococci getting into the body. Only rarely do meningococci overcome the body's defences and cause illness. There are a number of different groups of meningococci. There were over 2000 cases reported in the UK in 1998 and numbers have risen in the first few weeks of 1999. It is not known why some people become ill while others remain symptomless 'carriers' of the bacteria.
Infection can occur at any age.
However, most cases occur in children under four. The next highest incidence is recorded for teenagers between 15 and 19 years of age. In some poorer countries, such as in West and Central Africa and Iran, there are occasional epidemics. Someone with the infection will become very ill, though not all the symptoms will occur at once. A characteristic rash develops and may start as a cluster of pinprick blood spots under the skin, spreading to form bruises under the skin.