Six men in critical condition, with another 13 suspected cases being investigated amid hunt for source of outbreak

Seven men in Edinburgh have been confirmed as having legionnaires' disease, with another 13 suspected cases being investigated, as officials from the city council and Health and Safety Executive try to identify the source of the outbreak.

Six men between 30 and 65 are in critical condition in local hospitals. A seventh has recovered and been sent home, NHS Lothian said.

The first case was identified last Thursday, but symptoms can begin anytime between two days and two weeks after exposure to the legionella bacteria which causes the illness. Samples have been taken from four cooling towers in the south-west of Edinburgh, the seven confirmed cases have been geographically linked to the Dalry, Gorgie and Saughton areas of the city.

It might take up to 10 days before results are available, since legionella is difficult to culture. Meanwhile, those responsible for maintaining the towers have been advised to carry out additional chemical treatment to water in the systems as a precaution. Other possible sources are not being ruled out.

Duncan McCormick, consultant in public health medicine and chair of the incident management board, said: "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 problems 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."

Symptoms usually begin with a mild headache and muscle pain but become more severe after a day or two. These might include high fever, with a temperature of 40C (104F) or more, and increasing muscle pain and chills. Once the bacteria infects the lungs, carriers may also experience a persistent cough, later including mucus or blood, shortness of breath and chest pains. A third of people with the disease will experience nausea, vomiting, diarrhoea or loss of appetite and about half may also experience changes to their mental state.

Bacteriologist Hugh Pennington told BBC Radio Scotland said the disease was preventable. "Industrial water cooling towers are quite a common source of the bug. The bug lives in warm, fresh water. Basically disinfectant should be put in the water to stop the bug growing."

Legionnaires' was a "very, very severe pneumonia" but it was often hard to track down the source," he said. "If there are several water cooling towers in an area you have to look at them all and find out which is the source of the bug."

Lothian NHS said legionella bacteria could also find their way into air conditioning systems and hot water services. Legionnaires' disease was contracted by inhaling droplets of contaminated water but was not contagious and could not be spread directly from person to person.