THE Aneurin Bevan Health Board and Gwent councils are on alert following an outbreak of Legionnaires' disease.

The outbreak has seen a woman die of a suspected Legionnaires' disease infection with 11 other cases already confirmed, public health chiefs said today.

An investigation is under way in South Wales to find the source of the outbreak.

The 64-year-old woman, who has not been named, died yesterday and is an unconfirmed case of the disease.

"Public Health Wales (PHW), in collaboration with the Health and Safety Executive (HSE) and environmental health officers from seven South Wales local authorities, is investigating an outbreak of Legionnaires' disease clustered around the Heads of the Valleys corridor,’’ a PHW spokesman said.

"As of 7 September 2010, 11 cases had been identified as being linked to the outbreak and all required hospital treatment. A further three possible cases are under investigation.

"One of the possible cases under investigation, a 64-year-old female, died in hospital on 6 September.

"Investigations into the possible source of this outbreak are ongoing. Information has been circulated to GPs in the area advising of the steps to be taken if patients have symptoms.’’ Legionella bacterium has the potential to cause Legionnaires' disease which begins with flu-like symptoms and can lead to pneumonia. Most cases are sporadic and it generally occurs in adults.

Anyone who is concerned about their health should contact their GP.

Gwen Lowe, consultant in communicable disease control for Public Health Wales, said: "Legionnaires' disease is a rare but potentially life-threatening illness.

"Most of the cases of Legionnaires' disease that are notified to us are isolated cases, but outbreaks can occur,’’ she said.

"People become infected when they inhale Legionella bacteria which are spread through the air in the form of a fine mist or droplets from a contaminated water source.

"Legionnaires' disease cannot be passed from person to person.’’ A multi-agency outbreak control team has met to investigate the outbreak.

The team includes representatives from PHW, HSE, Cwm Taf Health Board, Aneurin Bevan Health Board, Cardiff and Vale University Health Board, Cardiff County Borough Council, Merthyr Tydfil County Borough Council, Rhondda Cynon Taff County Borough Council, Caerphilly County Borough Council, Blaenau Gwent County Borough Council, Torfaen County Borough Council and Monmouthshire County Borough Council.