The major sources of infection for Legionnaire's Disease, identified by study of outbreaks, are hot water systems and cooling towers. However, most cases are not part of outbreaks and, for these, the source of infection is rarely traced. The principal aim of this study was to help understand the source of non-outbreak infection by examining the epidemiology of the disease in Scotland. Of the recognized cases which met the study case-definition, 366 were ill between 1978 to 1986 giving a mean annual incidence rate of 7.9 per million. The annual incidence varied in Scotland (range 3.1 to 20.2) and within health boards. Geographical variations were demonstrated by health board, by city and within cities, particularly for non-travel infection. For example, the cumulative incidence rate per million for non-travel, non-outbreak disease in Greater Glasgow Health Board (GGHB) was 130 compared to 45 for the whole of Scotland, and 11, 33 and 50 in Tayside, Lanarkshire and Lothian Health Boards respectively. Of 16 postcode sectors with a high incidence of disease in Scotland, 14 were in GGHB. In GGHB, the residence of non-travel, non-outbreakcases (but not of travel-related ones) was clustered in central areas. Previously unrecognised clustering was also found in other health boards. These variations were not fully explained by differences in the population's exposure to diagnostic tests, as indicated by the number of serology tests requested by Scottish hospitals; the diagnostic service and approach of bacteriology laboratories; and the approach of hospital consultants to the diagnosis of Legionnaires' Disease. Differences in host susceptibility, as reflected by socio-economic status and the incidence of other respiratory disease, were small and did not explain the variation. In the City of Glasgow, many cooling towers were not maintained in accord with recommendations and posed a theoretical risk of infection. The location of residence of non-travel cases was associated with the location of premises with cooling towers, the incidence of non-travel Legionnaires' Disease being more than three times higher in areas of Glasgow within 0.5 kilometres of a cooling tower than in areas more than one kilometre away. The best explanation for these observations is that cooling towers were a major source of non-travel, non-outbreak infection. Hence, for the investigation and prevention of such infection, the emphasis should be on cooling tower maintenance. Close surveillance of apparently sporadic disease is recommended as the basis for disease control and future research.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:641600 |
| Date | January 1991 |
| Creators | Bhopal, Rajinder Singh |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/26329 |
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