Meningococcal disease is a serious illness, usually causing meningitis (inflammation of the lining of the brain) and septicaemia (blood poisoning). The disease is rare and affects between 200–250 people in NSW each year, which is less than 1 in 10 000 people. The bacteria that causes meningococcal disease is called meningococcus. There are several different types of meningococcus. In NSW, group B is responsible for about half of the cases of meningococcal disease, and group C is responsible for about one-third of cases.