Meningococcal disease describes infections caused by the bacterium Neisseria meningitidis (also termed meningococcus). It carries a high mortality rate if untreated but is a vaccine-preventable disease. While best known as a cause of meningitis, widespread blood infection can result in sepsis, which is a more damaging and dangerous condition. Meningitis and meningococcemia are major causes of illness, death, and disability in both developed and under-developed countries.