Meningococcemia is the presence of Neisseria meningitidis (also known as meningococcus), a severe bacterical infection, in the blood stream. It is demonstrated by blood culture.

The disease is hard to identify as it can appear in several different forms, depending on which part of the body the bacteria invade. There can be meningitis or septicaemia, or a combination of both.

Most cases of meningococcal meningitis occur in children. Early recognition and treatment of anyone exposed to meningococcus is extremely important to prevent serious illness or death. In cases of serious infection, sufferers may have to have limbs amputated as infected flesh dies off and may otherwise spread gangrene.