The Swansea coroner is investigating whether a 25-year-old man has died of measles. The city is at the centre of a major outbreak of the highly infectious disease, and the fatality – if the cause is confirmed – would be the first UK death from measles since 2008. Seventy-seven people have needed hospital treatment during the outbreak.

More than 800 cases, many among 10- to 18-year-olds, have been reported since November, and numbers are rising steadily and spreading north from the south of the country despite health authorities organising special immunisation clinics at hospitals and schools.

The man is being named locally as Gareth Williams. His body was found in a flat in the city on Friday. His death is not being treated as suspicious.

Health officials have repeatedly warned parents of children who had not had the triple measles, mumps and rubella (MMR) vaccine to arrange vaccination for them "as a matter of urgency".

One local head told the Guardian this week that he was concerned by a lack of response by some parents to a special clinic at his school.

Marion Lyons, director of health protection for Public Health Wales, said it was aware of a death being investigated by the Swansea coroner. She added: "A diagnosis of measles has not yet been confirmed. Testing the deceased for measles is forming part of the investigations being overseen by the coroner.

"My sympathies are with the family at such a tragic time. Whatever the cause of death in this case, we should not be surprised if, as the outbreak grows, we start to see deaths in Wales. Measles is a potentially fatal disease and around one in every 1,000 people who contracts measles in developed countries will die."

She added that those not fully vaccinated with two doses of MMR were likely to catch measles, which is highly contagious.

"We know that there are unprotected people in all age groups but we have particular concerns about the 10-to-18 age group," she said. "The MMR vaccine is recommended by the World Health Organisation, UK Department of Health and Public Health Wales as the most effective and safe way to protect children against measles.

"The alarming numbers of cases of measles and continuing spread of the disease in Wales illustrates how vital it is for parents to get their children vaccinated. Symptoms of measles include fever, cold-like symptoms, fatigue, conjunctivitis and a distinctive red-brown rash that appears a few days into the illness. Anyone who thinks they or their child may have measles should speak to their GP immediately."