Meningococcal disease is caused by Neisseria meningitidis, a gram-negative bacterium, and is an important cause of sepsis and meningitis. Worldwide, the most important serogroups of meningococci are groups A, B, C, W135 and Y. Groups B and C are the important types seen in children and young adults in New Zealand. Group A is an important epidemic strain, particularly in Africa and the Middle East. Serotype distribution patterns differ between countries. W135 and Y group organisms are seen as rare causes of bacteraemia and pneumonia in the elderly.
Spread from person to person is by respiratory droplets or direct contact with nasopharyngeal secretions, from a carrier or case.