Legionnaire's disease outbreaks are generally small and contained. (BBC)

An outbreak of Legionnaire's disease in Edinburgh has led to concerns about the potentially fatal illness spreading further in the UK.

However the illness, which has been confirmed in at least 17 people, is generally misunderstood and is normally found in a small number of cases, rather than widespread outbreaks.

What is Legionnaire's disease?

Legionnaire's disease is a form of lung infection [pneumonia] caused by a particular single bacteria. The disease is potentially deadly, with a fatality rate ranging from 5 to 30%. The majority of victims are in middle age or older.

The illness is severe, with antibiotic treatment essential. The last outbreak took place in Spain, infecting 18 people at a beach hotel and killing three.

The illness was given its name in1976 following an outbreak during an American Legion convention in Philadelphia. The bacteria that was found to have caused the illness was a new discovery, which was named legionella.

How is it caught?

The bacteria are present in natural water sources and grow best when the water is heated. This means that water tanks, air conditioning, hot tubs, cooling towers and even indoor fountains can become breeding grounds.

It is understood that infection generally takes place when a person inhales water droplets containing the legionella bacteria.

The risk of the bacteria being created has led to strict controls being placed on the maintenance of public water temperatures. Water must be kept either below 20C or heated to above 60C, to lower the outbreak risk.

What are the symptoms?

Legionnaire's disease can be a difficult illness to spot, with symptoms developiong anywhere between two to 20 days following exposure.

For the first couple of days, a sufferer woften reports muscle pain and some headaches. The symptoms will deteriorate over the next couple of days, leading to chills, fatigue, a high fever, increased muscle pain and altered (often confused) mental state.

The bacteria will continue to infect the lungs, often causing a persistent cough, which may lead to the sufferer coughing up blood. The cough will be accompanied by chest pains and shortness of breath.

How is it treated?

Once Legionnaire's disease is found, doctors will immediately administer antibiotics, such as erythrimycin, which can then be taken for several weeks as the sufferer fights off the disease.

People who have underlying health problems would be expected to be admitted to hsopital and given additional intravenous fluids and breathing support.

How common is it?

Legionnaire's disease outbreaks are generally found to take place in the summer and autumn and are swiftly contained once their source is discovered.

IN 2001 the world's largest outbreak of the disease took place in a hospital in Murcia, Spain, with 800 cases, from which three died.

The following year, an outbreak in Barrow-in-Furness led to 172 people being infected, seven of whom died. The outbreak was traced back to a contaminated cooling tower in the Forum 28 arts centre.

The last outbreak in the UK was in South Wales in 2010, when another contaminated cooling tower infected 22 people, two of whom died.