The number of people infected with measles has shot up by more than 78 in just than five days, health officials have confirmed.
Today Public Health Wales (PHW) revealed the total number of people who have contracted the disease in south west Wales now stands at 886.
Officials are urgently calling for more people to get vaccinated.
The fresh call comes following the death of a 25-year-old father-of-one from Swansea, who had the disease.
Dr Marion Lyons, Director of Health Protection for Public Health Wales, warned the current epidemic is showing no signs of ending.
"There is still an urgent need to vaccinate more children if we are going to end this outbreak," she added.
"The hardest hit age group is those between 10 and 18 so we would remind those young people and their parents that now is the time to be vaccinated.
"We have seen in the last few days that measles can be potentially fatal and no one should be complacent about the severity of measles. It can kill but can be prevented by a simple, safe vaccine."
PHW said its latest figures related to cases of measles between November 1 2012 and April 22 this year.
Of that total, 712 have been in the Abertawe Bro Morgannwg area while 99 were in the Hywel Dda region and 75 in Powys's health board zone.
Typical symptoms of measles include fever, cough, conjunctivitis and a rash. Complications are quite common even in healthy people, and about 20% of reported measles cases experience one or more complication.
These can include ear infections, vomiting and diarrhoea, pneumonia, meningitis and serious eye disorders.
Before the introduction of the MMR jab in 1988, about half a million children caught measles each year in the UK. Approximately 100 of those died.
While the latest epidemic is centred on Swansea, cases have continued to be reported across Wales.
With not enough "herd immunity", health officials had previously voiced concerns that it was just a matter of time before the disease claimed someone's life.
Last week, PHW revealed that tests are to be carried out on the body of Gareth Colfer-Williams, 25, who died at his home in Swansea last Thursday.
While Mr Colfer-Williams had measles, officials are still trying to establish whether it was the disease that killed him.
His mother, Angela, told BBC Wales how her son's fiancee, Cairo, had broken the news to the couple's daughter, Dakota.
"She just said that Daddy had to go away and had gone to heaven. Dakota started crying," she said.
"It's been awful. We're all trying to be very upbeat with her."