The majority of meningococcal disease occurs in infants less than five years of age, with a peak incidence in those under 1 year of age. There is a smaller, secondary peak in incidence in young adults aged between 15 - 19 years of age.
Most cases of meningococcal disease occur sporadically, with less than 5% of cases occurring in clusters. Outbreaks of meningococcal disease are more common among teenagers and young adults, and outbreaks have been reported in schools and universities. Public health interventions may include vaccination (depending on serogroup) and chemoprophylaxis.
Meningococcal disease shows marked seasonal variation with a peak in winter and a low level in summer. The winter season coincides with that of influenza. (see News and Events, Seasonal Diseases)
Meningococci are divided into distinct serogroups, according to their polysaccharide outer capsule. The most common serogroups that cause disease worldwide are groups B, C, A, Y and W135. Prior to the introduction of Men C vaccine, most disease in the UK was caused by serogroups B and C.
However, the number of cases caused by serogroup C have significantly reduced in all age groups since routine Men C vaccination was introduced (see Vaccination against Meningococcal disease) and serogroup B now accounts for 85-90% of all cases of meningococcal disease.
Meningococcal disease has an overall case fatality rate of approximately 10%, however this varies by a number of factors, including serogroup, age, and prompt antibiotic treatment. More deaths are caused by septicaemia than by meningitis.
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