Meningococcal disease occurs worldwide. N. meningitidis sero-group A usually causes epidemics, serogroup B causes both epidemics and outbreaks, while serogroup C mostly causes localized outbreaks. Endemic meningitis is more common in children below the age of 5 years and in elderly people. Large outbreaks of meningococcal disease have occurred in central African countries with attack rate as high as 400–500 cases per 100,000 population. Epidemics of meningococcal disease have occurred in many parts of the world.
Meningococci of group A are associated with diseases in underdeveloped countries; meningococci of group B, C, or Y are responsible for most (90%) of the cases of meningococcal diseases in the developed countries (Table 26-5).
N. meningitidis is primarily a pathogen of humans. Meningococciare found in the nasopharynx and oral cavity. Asymptomatic carriage of N. meningitidis varies from as low as 1% to as high as 40% in the population. The carriage rates are highest in school-going children, in young adults, and in the population with low economic status.
Human is the only reservoir of meningococcal infection. Nasopharyngeal secretion is the most common source of infec-tion. Meningococci are transmitted by airborne droplets of infected nasopharyngeal secretions (the most common source of infection). Family members living in crowded conditions or the people who live in close populations (such as military barracks and prisons) and older people are more susceptible to infection.