Meningococcal disease in New South Wales, 1991-2002.

Meningococcal disease is caused by invasive infection with the bacteria Neisseria meningitidis. Humans are the only natural reservoir for N. meningitidis, 5–10 per cent of whom have naso-pharangeal colonisation of the bacteria at any given time. The bacteria are transmitted between people by secretions from the naso-pharynx. Disease occurs in rare instances when a virulent strain of the bacteria invades through the naso-pharynx. Disease can present in a variety of syndromes, usually meningitis and/or septicaemia, and more uncommonly pneumonia, otitis media, septic arthritis, urethritis, and purulent pericarditis.