Meningococcal disease (septicaemia and/or meningitis) is caused by a Gram-negative bacterium, Neisseria meningitidis (the meningococcus), which is spread from person to person through respiratory droplets.
Meningococci are classified according to the chemical structure of their capsular polysaccharide. Meningococci of 6 of the 12 recognised meningococcal serogroups (A, B, C, W, X and Y) cause invasive meningococcal disease.
Meningococci within a specific serogroup can be characterised further by additional laboratory techniques including Multi Locus Sequence Typing (MLST).
Epidemics of meningococcal disease in Africa are usually caused by meningococci belonging to serogroup A, although outbreaks caused by meningococci belonging to serogroup W or serogroup X have been recorded recently in Burkina Faso and Niger respectively.
In European countries, the annual incidence rate of meningococcal disease varies between 1.0 and 5.0 per 100,000 inhabitants. In contrast, the world’s highest incidence rates of meningococcal disease (up to 1000 per 100,000 inhabitants) are reported during epidemic periods in countries situated in the meningitis belt, an area that stretches across Africa from Ethiopia in the east to The Gambia and Senegal in the west.