Festival-goers in England have been urged to ensure they are vaccinated against measles after a "significant number of cases" were linked to popular events there this summer.
There have been a number of suspected cases picked up at popular festivals including Glastonbury, officials said.
Large events where people are in close proximity to one another "provide the ideal place for the infection to spread", Public Health England (PHE) said.
PHE has urged young people attending events to get their MMR vaccination.
Anyone who thinks they may have the infection should not attend upcoming events as they may pass it on, it added.
The health body said there have been dozens of suspected measles cases reported in people who attended events in June and July.
Dr Mary Ramsay, head of immunisation at PHE, said: "Measles is a highly infectious viral illness that can be very unpleasant and sometimes lead to serious complications. So, if you think you might have measles, please don't go to any of these big events.
"Measles isn't common these days because most of us are vaccinated, but young people who missed their MMR jab as children are vulnerable, especially if gathered in large numbers at an event.
"If you think you've got it, call your GP or NHS 111. Please don't turn up at the surgery or at A&E as you could infect other patients."
Cases of measles have been linked to:
:: Glastonbury festival - 16 cases.
:: NASS festival - seven cases.
:: Triplicity Music and Arts Festival - six cases.
:: Tewkesbury Medieval Festival - three cases.
:: Nozstock: The Hidden Valley - two cases.
:: Noisily Festival - two cases.
:: Secret Garden Party festival - one case.
:: Yeovil Show - one case.