The bacteria only rarely give rise to meningococcal disease, but when they do infection spreads rapidly and is fatal in about 10% of cases. If disease is diagnosed early and treated promptly most people make a full recovery.
About 1 in 8 people who recover experience some long term effects. These can include headaches, stiffness in the joints, epileptic fits, deafness and learning difficulties.
More top news
Owen Lambert, 18, and his friends were on a university trip to Parliament when they were hit by the Westminster attacker's speeding car.
Teenage blogger Amos Yee from Singapore was jailed for posting criticisms of his government online.
Supermarket chain decide to unlock trolleys at some of its biggest stores as it deals with the implications of the new £1 coin rollout.