Research
Feasibility and utility of mapping disease risk at the neighbourhood level within a Canadian public health unit: an ecological study
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* Corresponding author: Eric J Holowaty eric.holowaty@cancercare.on.ca
- † Equal contributors
1 Population Studies and Surveillance, Cancer Care Ontario, 620 University Avenue, Toronto, Ontario, Canada
2 Dalla Lana School of Public Health, University of Toronto, 155 College St., Toronto, Ontario, Canada
3 CIBER Epidemiología y Salud Pública (CIBERESP) and Centre for Public Health Research (CSISP), Valencia, Spain
4 Small Area Health Statistics Unit, MRC-HPA Centre for Environment and Health, Imperial College London, UK
International Journal of Health Geographics 2010, 9:21 doi:10.1186/1476-072X-9-21
Published: 10 May 2010Abstract
Background
We conducted spatial analyses to determine the geographic variation of cancer at the neighbourhood level (dissemination areas or DAs) within the area of a single Ontario public health unit, Wellington-Dufferin-Guelph, covering a population of 238,326 inhabitants. Cancer incidence data between 1999 and 2003 were obtained from the Ontario Cancer Registry and were geocoded down to the level of DA using the enhanced Postal Code Conversion File. The 2001 Census of Canada provided information on the size and age-sex structure of the population at the DA level, in addition to information about selected census covariates, such as average neighbourhood income.
Results
Age standardized incidence ratios for cancer and the prevalence of census covariates were calculated for each of 331 dissemination areas in Wellington-Dufferin-Guelph. The standardized incidence ratios (SIR) for cancer varied dramatically across the dissemination areas. However, application of the Moran's I statistic, a popular index of spatial autocorrelation, suggested significant spatial patterns for only two cancers, lung and prostate, both in males (p < 0.001 and p = 0.002, respectively). Employing Bayesian hierarchical models, areas in the urban core of the City of Guelph had significantly higher SIRs for male lung cancer than the remainder of Wellington-Dufferin-Guelph; and, neighbourhoods in the urban and surrounding rural areas of Orangeville exhibited significantly higher SIRs for prostate cancer. After adjustment for age and spatial dependence, average household income attenuated much of the spatial pattern of lung cancer, but not of prostate cancer.
Conclusion
This paper demonstrates the feasibility and utility of a systematic approach to identifying neighbourhoods, within the area served by a public health unit, that have significantly higher risks of cancer. This exploratory, ecologic study suggests several hypotheses for these spatial patterns that warrant further investigations. To the best of our knowledge, this is the first Canadian study published in the peer-reviewed literature estimating the risk of relatively rare public health outcomes at a very small areal level, namely dissemination areas.