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.
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Sunny and dry for most on Monday although rain affects much of Ireland.
The band returned to the festival - a decade after a disastrous set - as the iconic festival drew to a close on Sunday.
The band dedicated their song Everlast to fan Laura Plane, who died from breast cancer last month.