Meningococcal Meningitis

Meningitis caused by N. meningitidis occurs sporadically in small clusters throughout the world and accounts for a variable proportion of endemic bacterial meningitis. In temperate regions the number of cases increases in winter and spring. It is estimated that 5–10% of a population may be carriers of N. meningitidis at any one time in a non-epidemic situation.¹ Meningitis caused by N. meningitidis is particularly important as this bacterium has the ability to cause disease epidemics.

Five different serogroups of N. meningitidis are responsible for causing disease (serogroups A, B, C, W-135 and Y); the incidence and relative contribution of the five serogroups differs regionally. Serogroups C and B are responsible for the majority of cases in Europe and accounted for 95% of all cases in Europe in 1999 and 2000f. Out of serogroups C and B, group B is the more frequently seen, accounting for 63% of all cases in Europe from 1999 to 2000f. Serogroup B is most dominant in Denmark, Germany, the Netherlands, Norway and the UK, while serogroup C is responsible for a high proportion of cases in the Czech Republic, Greece, Ireland, Slovakia and Spain. Serogroup Y is responsible for 1.3% of the total number of cases of meningococcal meningitis in Europe, but its relative contribution is much higher in other places in the world; for example serogroup Y is responsible for 20% of cases in Israel.²

Serogroup A meningococcus causes large-scale epidemics in developing countries but rarely causes disease in Europe (where it was responsible for 0.3% of the total number of cases of meningococcal disease in 1999 and 2000).² However, although the incidence of disease caused by this serogroup is low overall in Europe, it has a higher relative contribution in particular countries in Europe; for example, serogroup A accounted for >10% of all cases of meningococcal disease in Greece and Romania between 1999 and 2000f. Serogroup A is the major cause of epidemic and endemic meningococcal disease in Africa, especially in an area known as the ‘meningitis belt’.

Recently, serogroup W-135 has also caused epidemics of meningococcal disease and has been a particular problem in travellers, for example people taking part in the Hajj pilgrimage in Saudi Arabia.  Epidemics of Group B meningococcal disease have occurred in Norway, Brazil, Chile, Colombia, Cuba and New Zealand. In the latter, disease incidence has been particularly high in Pacific Islanders and Maori populations.

Meningococcal meningitis mainly affects infants and young children but can infect older individuals. Adolescents are also particularly at risk from this disease due to their living conditions and social activities (see section on Risk Factors).