Meningococcal disease is an infection caused by bacteria.
The bacteria can live in the membranes of the nose and throat, usually with no symptoms. In a small number of people, the bacteria passes to the blood, causing either a serious infection of the blood or meningitis. Babies, children and young adults are most likely to get the disease. People living in crowded places are at higher risk for infection. Outbreaks usually do not occur in school or workplace settings.