Meningitis is an infection of the protective membranes that surround the brain and spinal cord, according to NHS Choices.
They say: "It can affect anyone, but is most common in babies, young children, teenagers and young adults.
READ: Two cases of meningitis confirmed at NI primary school
Meningitis can be very serious if not treated quickly. It can cause life-threatening blood poisoning (septicaemia) and result in permanent damage to the brain or nerves.
A number of vaccinations are available that offer some protection against meningitis."
According to NHS Choices meningitis is usually caused by a bacterial or viral infection - and can be spread through:
sharing utensils, cutlery and toothbrushes
Meningitis is usually caught from people who carry these viruses or bacteria in their nose or throat but aren't ill themselves.
It can also be caught from someone with meningitis, but this is less common.
READ: Overview on Meningitis