Update On Legionnaires Disease 23 August 2005
The Canterbury District Health Board today announced that four Christchurch businesses yielded positive results when their cooling towers were tested for possible contamination that could result in Legionnaires Disease.
Canterbury Medical Officer of Health Dr Mel Brieseman said public health teams were working closely with the organisations to assess the significance of the results.
‘Although all companies with cooling towers in the city haven’t yet completed their checks and we are still waiting for results, we are treating these first results very seriously.’
Dr Brieseman said he was not yet in a position to identify the companies which came from across the industry sector and were situated in different parts of the city.
‘We are taking an industry-wide approach on this issue and have received tremendous support from the sector to date as well as the City Council and the Chamber of Commerce.’
Dr Brieseman said because of the widespread nature of the legionella organism in the environment some positive results were not surprising as a small number of bacteria could easily enter any water supply. In addition, he said, there were 40 types of legionella organism and 18 sub-types of the particular strain which has caused the recent outbreak of cases.
‘The significance of a positive test is therefore dependant on determining not only the specific strain of the organism isolated from a cooling tower, but the number of likely organisms and their potential for spread from a particular site.’
‘What we must be aware of in this particular situation is that there are many options for the legionella bug to develop and while we have been concentrating on cooling towers we have also been exploring other options.’
Dr Alistair Humphrey who has been leading a controlled case study into the outbreak yesterday completed the survey of the 16 patients, the families of the three patients who have died, and 57 randomly selected controls.
Dr Humphrey said the study looked in detail at risk factors for the outbreak of Legionnaires such as where they lived, what their health conditions were, their ages, lifestyle, and so on. This was compared against the other people in the study who were not identified as having had Legionnaires Disease.
The study has excluded a number of important risk factors. For example, there is no relationship between any hospital and this outbreak. There is no relationship in this outbreak with hot water supplies. However, the study has confirmed that elderly and/or debilitated people living in certain parts of Christchurch have been more at risk.
‘By excluding the hospital, we can now investigate the spatial relationship between cases and controls,’ he said. ‘The study has identified that there is a spatial relationship between the cases here, and we will investigate this further in the second arm of the study.’