One man has died and 15 people are in a critical condition in hospital following an outbreak of Legionnaires' disease.

A further 15 suspected cases are being investigated in Edinburgh, NHS Lothian said.

The health board said the patient who died was in his 50s and had underlying health conditions. He was being being treated at the Royal Infirmary of Edinburgh.

Thirteen men and two women aged between 33 and 74 are in a critical condition with the disease and are being treated in intensive care in hospitals in the Lothian area. One man has recovered and has been discharged.

A further 10 men and five women are also being treated in hospitals but their illness has not yet been confirmed.

The majority of the confirmed cases are linked geographically to the Dalry, Gorgie and Saughton areas in the south west of the Scottish capital.

Health Secretary Nicola Sturgeon will chair a meeting of the Scottish Government's Resilience Committee this morning, where she will be updated on the situation and on efforts to identify the source.

Dr Duncan McCormick, consultant in public health medicine and chairman of the incident management team at NHS Lothian, said: "I would like to express my sincere condolences to the family of the patient that died.

"Investigations into the possible source of this outbreak are on-going. Meanwhile, medical staff have been actively identifying possible cases to allow us to ascertain the full extent of this outbreak.

"I would like to reassure the public that household water supplies are safe and that Legionnaires' disease cannot be contracted by drinking water.

"Older people, particularly men, heavy smokers and those with other health conditions, are at greater risk of contracting the disease. I would urge anyone who develops symptoms of Legionnaires' disease to contact NHS 24 or their GP."

The health board said Legionella bacteria is commonly found in sources of water, such as rivers and lakes.

The bacteria can end up in artificial water supply systems, including air conditioning systems, water services and cooling towers.

Legionnaires' disease is contracted by breathing in small droplets of contaminated water.

Symptoms include mild headaches, muscle pain, fever, a persistent cough and sometimes vomiting and diarrhoea, and can begin any time between two and 14 days after exposure to the bacteria. The first case was identified on Thursday May 28.

About half of those who contract the disease will also experience changes to their mental state, such as confusion.

The condition is not contagious and cannot be spread directly from person to person.

A Scottish Government spokesman said: "Our thoughts are with patients and their families at this time and, in particular, with the family of the patient who has very sadly died.

"NHS Lothian and Health Protection Scotland are taking all appropriate steps to manage this situation and are working closely with Edinburgh City Council and the Health & Safety Executive to identify the source as quickly as possible.

"A number of cooling towers in the area have already been subject to chemical treatment.

"The Health Secretary - who has been kept closely informed of all developments - will chair a meeting of the Scottish Government's Resilience Committee tomorrow morning, at which she will be further updated on the situation and on the progress of efforts to identify the source.

"The Scottish Government would like to reassure the public that everything possible is being done to identify the source and anyone with health concerns is advised to contact NHS 24 or their GP."

Shadow Scottish Health Secretary Jackie Baillie also added her condolences.

She said: "Our thoughts and prayers are with the family of the man who has sadly lost his life.

"We must now find out the source of this outbreak as quickly as possible to ensure it is contained and there are no other victims."

The source of the outbreak is being investigated by officials from the City of Edinburgh Council's Environmental Health Department and the Health and Safety Executive.

Samples have been taken from cooling towers in the south west of the city, though it may be up to 10 days before results are available as Legionella is a difficult bacteria to culture.

Those responsible for maintenance at the cooling towers have been advised to carry out additional chemical treatment to the water in the cooling systems as a precautionary measure.

The health board said other possible sources were not being ruled out.