Humans are the only known reservoir for meningococcus. Around 10% of adults and 25% of adolescents are colonised with the bacteria in the nasopharynx, and are asymptomatic. In younger children carriage rates are much lower[24,25].
Transmission is by aerosol, droplet, or direct contact with respiratory secretions of someone carrying the organism, usually with frequent or prolonged close contact.
Incidence of meningococcal disease is highest in children under five years of age, peaking in those under one year old. There is a secondary smaller peak in young people aged 15 to 19 years old. There is marked seasonal variation, with case numbers peaking in the winter months.
Since the introduction of vaccination programmes, mortality from meningococcal disease has fallen from 10% to 5%, though this is higher in individuals with septicaemia than meningitis alone[24,25].