Parents are urged to ensure their children have been vaccinated
Four children have been treated in hospital after contracting measles, the National Public Health Service (NPHS) has said.
The children aged under two, went to a nursery in the Burry Port area of Carmarthenshire but are now home. Another 32 have since been vaccinated.
Official figures show 127 cases of measles have been reported in mid and west Wales in recent weeks.
Parents are urged to ensure their children are vaccinated.
Officials have said a special session, to vaccinate 32 people who had come into contact with the four children, was held on Friday evening.
Dr Marion Lyons says this is the biggest caseload of measles they've dealt with in Wales for a decade
Four different outbreaks of measles account for 69 of the cases in Mid and West Wales with 14 cases related to an outbreak in South Pembrokeshire, 46 cases in Llanelli, four in Burry Port and five in Neath Port Talbot.
Cases are occurring across all age groups from children as young as five months to adults in their late 40s.
The other 58 cases are sporadic cases with no clear connection to the three outbreaks.
They are broken down as: Six cases in Pembrokeshire, six in Carmarthenshire, four in Ceredigion, two in Powys, 17 in Swansea, eight in Neath Port Talbot and 15 in Bridgend.
Dr Mac Walapu, consultant in Communicable Disease Control for the NPHS, said: "For as long as there are children who do not receive their MMR vaccinations, there is the potential for outbreaks of measles to happen and we would remind anyone in Wales, and not just in the affected area.
"There is no evidence of any child being harmed by the MMR vaccination but there is strong evidence that as many as one in 500 children who catch measles will die, and that another one in 500 will suffer permanent brain damage.
"With so many cases in the community, any child who has not received vaccination is at risk and parents must be aware of the potential consequences of not arranging immunisation for their children."
Last week, he expressed alarm at seeing so many measles cases at one time, while he said in some schools the MMR uptake was as low as 14.8%.
Latest figures show that 86% of two-year-olds in Wales have been given the MMR vaccine, ranging in different areas from 78% to 92%.
This is short of the 95% target which has already been achieved in Scotland. The figure for England is around 85%.
Official advice is that children should receive their first dose of the vaccine at the age of one and the second before they start school, and anyone in Wales who is older than this and has not received the full two doses of the vaccine should come forward for immunisation.
Dr Walapu added: "If your child is unwell and you suspect it is measles, you should contact your GP. Your child should not attend school or nursery for five days after the rash starts."
Many people who catch measles will have a fever, a rash and feel generally unwell. Typically, people will be infectious from a few days before the onset of their rash until four to five days after the onset of the rash.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.