AS many as 20 people could die in what is expected to become the UK's biggest outbreak of Legionnaire's disease, hospital chiefs said last night.

One elderly man has already died from the virulent form of pneumonia.

The 89-year-old, who has not been named, was among 19 confirmed cases of the disease reported in the Cumbrian town of Barrow-in-Furness.

Fifteen more people are suspected to have the disease, and 130 are expected to be admitted to hospital over the next fortnight. Between 15 and 20 could die.

Last night, urgent efforts were under way to establish the source of the disease, which is often spread via water in air-conditioning systems.

Forum 28, a council-run leisure centre opposite the Town Hall, was closed yesterday as a precautionary measure. Water samples were taken from the centre and the site was cordoned off by police.

Dr Nigel Calvert, a consultant in communicable disease control who is in charge of the investigation into the outbreak's source, told a press conference: "This is the largest outbreak I am aware of."

He said that anyone who had visited Barrow since July 1 could have contracted the disease and if they displayed any pneumonia-like symptoms they should contact their GP.

Asked if people should avoid the centre of Barrow, Dr Calvert said: "It's difficult to give cast iron advice. We are doing our best to find a solution."

People with the disease are being treated at Furness General Hospital in the town.

Dr Frank Atherton, director of public health for Morecambe Bay Primary Care Trust, said: "People could still be exposed to the infection. There's going to be a great deal of public concern."

Legionnaires' disease got its name in 1976 when there was an outbreak of pneumonia among people attending an American Legion Convention in Philadelphia. Twenty-nine people died.

The disease is a form of pneumonia caused by bacteria which live in water droplets.

It breeds in warm, moist conditions and in most major outbreaks the source of infection has been the water in the air-conditioning system in large public buildings.

Young people generally make a full recovery, but elderly or unfit people can die from the illness.

A spokeswoman for the Public Health Laboratory Service said there were up to 200 cases of Legionnaires' disease each year.

There have been at least two cases of the disease in the North-East and North Yorkshire in the last two years.

Jim Stevens, a teacher from North Yorkshire, died in a York hospital in 2000 after returning from a long weekend in Germany.

Jimmy Harrison, 44, from Hartlepool, spent more than ten days in intensive care in the town fighting off the crippling symptoms last summer.