Legionnaires' disease outbreak in Edinburgh expected to spread Legionella bacteria, which cause legionnaires' disease. Health officials in Edinburgh expect the legionnaires' disease outbreak in Edinburgh to spread further over the next few days after the death of a man in his 50s. Speaking after the number of confirmed and suspected cases reached 30 on Tuesday, specialists with NHS Lothian said they were anticipating more cases over the next few days before the peak of the outbreak was reached. There were 15 people in a critical condition in hospitals around Edinburgh by Tuesday night, with a further 15 suspected cases under investigation. Dr Duncan McCormick, the chair of NHS Lothian's incident management team, said it probably would take until the weekend before the true scale of the outbreak became clear, because the bacteria can have a long incubation period. He said "shock treatment" had now been used on 16 industrial cooling towers in south-west Edinburgh, thought to be the most likely sources of the outbreak, to eradicate the waterborne bug. Speaking to the BBC on Wednesday morning, McCormick said: "The incubation period of legionnaires' disease is between two and 14 days but the average is five or six days, so we're expecting to have more cases over the next few days. But if our evidence and reaction have been correct, we hope to have removed the source through our shock treatment of these cooling towers. We'd hope that by the weekend - five or six days after the treatment - we'll start to see a decline in cases. The Scottish government has convened its resilience committee to oversee the handling of the outbreak, which has included environmental health officers from City of Edinburgh council. Officials are still not certain what the source of the outbreak is, and believe the potential area of infection - believed to centre on south-west Edinburgh where the majority of patients live - could cover 44 square miles. Doctors across the city have been issued with fresh guidance on the Legionella bacterium and asked to be alert for fresh cases. But McCormick has played down the risks for residents of Gorgie, Dalry and Saughton, dismissing any fears that the water supply is contaminated. Nicola Sturgeon, the Scottish health secretary, told BBC Radio Scotland she too was expecting further cases to emerge in the next two days. Over the next few days we will be ensuring that the public has all the right information. The message to the public is firstly that the risk to the general population is low. "Clearly, as with many conditions, there is a higher risk with people who have underlying health conditions," she said.