Almost 30 suspected cases of mumps - a contagious viral infection that causes swelling of the glands - have struck students at universities in Wales.
Public Health Wales (PHW) is investigating a series of cases in Cardiff and the Cwm Taf area.
It is urging people to make sure they have received the MMR vaccination.
Cardiff University, Cardiff Metropolitan University and the University of South Wales have advised students to be aware of symptoms.
PHW has been informed of 28 suspected cases, as of 16 October, though said it was continuing to monitor the situation.
Nah who's the antivaxx kids that's caused this mumps outbreak at Cardiff uni then?? More people in my house are getting diagnosed with mumps— kierra (@kierramarie99) October 15, 2019
Just three weeks into the new academic year, Cardiff Metropolitan University, which saw a similar outbreak in April, said it was aware of a number of cases and was supporting those affected.
The University of South Wales has asked anyone diagnosed with the virus to contact staff, while Cardiff University said it was unaware of any cases among its student population but said the position remained "changeable".
People have been advised to make sure they are up to date with their MMR vaccination against measles, mumps and rubella.
Immunisation rates have been falling for a number of reasons and the UK has lost its measles-free status.
But while the MMR jab provides 99% protection against measles, PHW said it only provided immunity against mumps to about 85% of recipients.
Rhianwen Stiff, a consultant in communicable disease control for PHW, said: "It is possible to see mumps in individuals who have been vaccinated with MMR.
"Mumps is spread by coughs and sneezes and directly through contact with the saliva of an infectious person such as through sharing drinks or kissing.
"It is important that people with suspected mumps keep away from university and social gatherings for five days after their symptoms start, wash their hands frequently and especially after blowing their nose and don't share items such as water bottles or cigarettes with others."
Mumps is most recognisable by the painful swellings at the side of the face under the ears.
Other symptoms before the swelling may include:
- joint pain
- loss of appetite
- feeling sick
- painful swelling of the testicles or ovaries
- high temperature
Anyone with these symptoms is advised to see their GP.
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