Music festivals including Glastonbury have become a hotbed of measles this summer, Public Health England has warned.
It said a “significant number” of cases had been linked to the events, with 36 cases reported in June and July alone.
More infected people are expected to be discovered as the outbreaks are investigated.
People planning to attend other festivals are advised to ensure they are vaccinated against the disease.
Measles is a highly-infectious virus which causes a rash and cold-like symptoms for most people, but it can be deadly.
Public Health England describes festivals as the “ideal place” for the infection to spread because of the large numbers of people mixing together.
The cases were 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
At least three people are known to have developed symptoms, but decided to go to the gatherings anyway.
In a statement on the Public Health England website, Dr Mary Ramsay 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.”
The festival outbreaks come as the measles virus is spreading more readily in England.
There were only 54 cases in the first half of 2015, but there have been more than four times that number – 234 – in the first six months of this year.
Some have needed hospital treatment.
Most of the festival-related cases were in people who had not been vaccinated.
MMR (measles, mumps and rubella) immunisation rates are now at record levels in children.
But now completely discredited claims by Andrew Wakefield of a link between MMR and autism, led to vaccination rates falling to 80% by 2005.
It left a large number of people vulnerable to measles – in 2013, an outbreak in Swansea led to 1,219 people being infected.
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Measles – what to look for:
- cold-like symptoms, such as a runny nose, sneezing, and a cough
- sore, red eyes that may be sensitive to light
- a high temperature (fever), which may reach around 40C (104F)
- small greyish-white spots on the inside of the cheeks
- a few days later, a red-brown blotchy rash