Meningococcal disease includes meningococcal meningitis and meningococcaemia. Meningococcal meningitis is a severe bacterial infection of the membrane that covers the brain and spinal cord. Meningococcaemia is an infection of the blood. Meningococcal meningitis and meningococcaemia are caused by the bacterium Neisseria meningitidis (N. meningitidis), which is known as the meningococcus and infects humans only.