Abstract
OBJECTIVES: Although individuals living in areas with lower household income have been shown to have higher rates of mortality from colorectal cancer (CRC), findings on the effect of income on CRC incidence in countries with universal health care have been inconsistent. There are limited data from Canada. We investigated the geographic variation and factors associated with CRC incidence in Manitoba, a central Canadian province.
METHODS: The Manitoba Cancer Registry and Manitoba Health population registry were used to determine age-sex-standardized CRC incidence rates between 1985 and 2012, which were geocoded to 498 small geographic areas (SGAs). The 2001 Canadian Census was used to determine the socio-demographic characteristics of the SGAs. Bayesian spatial Poisson modelling was used to assess geographic variation and factors associated with CRC incidence.
RESULTS: CRC incidence in SGAs ranged from 11 to 1026 per 100 000 population per year. Importantly, in the fully adjusted model there was no significant association between either average household income or proportion of recent immigrants in the SGAs and CRC incidence. Individuals living in urban areas had an overall lower CRC incidence (incidence rate ratio: 0.76; 95% credible interval: 0.58–0.98).
CONCLUSIONS: In a province with a universal health care system, our study suggests there are no disparities in CRC incidence by socio-economic level of the areas of residence. Rural areas should be a focus of CRC reduction initiatives in Manitoba. Similar analysis in other jurisdictions should be performed to evaluate the effect of the characteristics of SGAs on CRC incidence in different settings and target some of the efforts to reduce CRC burden.
Key words: Epidemiology, spatial analysis, variation in risk, disparities
Résumé
OBJECTIFS: Il a été démontré à maintes reprises que les résidents des zones où le revenu des ménages est faible présentent des taux de mortalité due au cancer colorectal (CCR) plus élevés, mais l’effet du revenu sur l’incidence du CCR dans les pays dotés d’un système de soins de santé universel ne fait pas l’unanimité. Les données du Canada en la matière sont limitées. Nous avons étudié la variation spatiale de l’incidence du CCR et les facteurs associés au Manitoba, une province du centre du Canada.
MÉTHODE: Le Registre du cancer du Manitoba et le registre de la population de Santé Manitoba ont servi à déterminer les taux d’incidence du CCR standardisés pour l’âge et le sexe entre 1985 et 2012; ces taux ont ensuite été géocodés selon 498 petites régions géographiques (PRG). Le Recensement du Canada du 2001 a servi à déterminer le profil sociodémographique de ces PRG. Un modèle bayésien d’analyse de données spatiales et de régression de Poisson a servi à évaluer la variation spatiale de l’incidence du CCR et des facteurs associés.
RÉSULTATS L’incidence du CCR dans les PRG variait de 11 à 1 026 pour 100 000 habitants par année. Il est important de noter que dans le modèle entièrement rajusté, aucune association significative n’a été observée entre le revenu moyen des ménages ou la proportion d’immigrants récents dans les PRG, et l’incidence du CCR. Les résidents des agglomérations urbaines présentaient dans l’ensemble une plus faible incidence de CCR (rapport de taux d’incidence: 0,76; intervalle de crédibilité de 95 %: 0,58–0,98).
CONCLUSIONS: Dans une province dotée d’un système de soins de santé universel, notre étude indique qu’il n’y a aucune disparité dans l’incidence du CCR selon le niveau socioéconomique des régions de résidence. Les milieux ruraux devraient faire l’objet d’initiatives de réduction du CCR au Manitoba. Des analyses semblables devraient être effectuées dans d’autres collectivités publiques pour évaluer l’effet des caractéristiques des PRG sur l’incidence du CCR dans différents milieux et pour cibler une partie des efforts de réduction de la charge de morbidité de ce cancer.
Mots clés: épidémiologie, analyse spatiale, variation du risque, disparités
Footnotes
Conflict of Interest: H. Singh has been on the advisory board of Pendopharm and Ferring Canada and has received research funding from Merck Canada. J. Samaddar has been on scientific advisory boards for Janssen Pharmaceuticals and Cancer Prevention pharmaceuticals and has been a speaker for Cook Medical Inc. The other authors declare no conflict of interest.
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