Environmental health workers have been cleaning water-cooling towers in an area of Edinburgh after an outbreak of legionnaires' disease.
Six people were confirmed as having contracted the disease and four others are suspected cases.
At least three of the people infected are being treated in intensive care and one is in a high dependency unit. All are said to be "very poorly".
Tests are being carried out on the four suspected cases - two women aged 49, and two men, aged 88 and 63.
All those affected are from an area covering Gorgie, Saughton and Stenhouse to the southwest of Edinburgh city centre. A total of 16 cooling towers in the area have been disinfected by environmental health workers.
A spokesman for NHS Lothian said they believe that bacteria had entered the atmosphere from a water cooling unit in the vicinity.
Duncan McCormick, a consultant in Public Health Medicine for NHS Lothian, told Sky News: "Anybody who develops symptoms of legionnaires' disease should contact NHS 24 on 08454 24 24 24 immediately or go to their GP.
"The safety of the public is our number one priority and we would urge people to look out for the symptoms of this disease."
Legionnaires' disease is contracted by breathing in small droplets of contaminated water.
However, the condition is not contagious and cannot be spread directly from person to person.
Large buildings such as hotels, hospitals, museums and office blocks, are more vulnerable to legionella contamination because they have larger, more complex water supply systems, in which legionella contamination can quickly spread.
Symptoms usually begin with an initial phase lasting 1 to 2 days, in which you experience mild headaches and muscle pain.
This is followed by the onset of more severe symptoms including high fever, usually a temperature of 40C (104F) or above, more severe muscle pain, and chills.