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Six recent cases of Legionnaires disease have been linked to an industrial cooling tower in the Canterbury area.
Dr Raymon Pink, medical officer of health for the Canterbury region, said the first cases were notified in April.
Two new cases were notified in May.
There had been no more cases since May 25.All of the patients were hospitalised, with their time in hospital averaging six days. None of the patients needed intensive care.
Symptoms of the respiratory illness were influenza-like.
Two of the patients didn't live in the area but had been visitors there. For that reason it took a while to identify the cluster.
The cases were linked to a cooling tower in the Hillsborough area which had since tested positive for Legionella.
The tower was treated immediately and subsequent testing showed it was clear of the disease.
The District Health Board had been working to encourage the industry to test and treat cooling towers, said Dr Pink.
The two cases which occurred in May occurred after the cooling tower had been treated. That raised the question of whether the original cooling tower seeded other cooling towers or vice versa.
"Our working hypothesis is that it is most likely to be a cooling tower or cooling towers that have caused this cluster."
Dr Pink said the risk for people going into the area was "absolutely minimal".
"I think there'd be more danger driving your car than there would be of getting Legionella's disease in this situation. I can't say there is completely no risk but I would say that the risk is extremely low."
Those working in the area hadn't been informed about the disease until today. That was because the risk was low and the cases were unseasonal.
"There's always a balance between trying to inform the public but also not to cause anxiety that's unnecessary," said Dr Pink.
People over the age of 50 were more vulnerable to the disease, particularly those with comorbidities.
'It’s been a tough year and now we feel like we can breathe.'