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EPIDEMIOLOGY


PREVALENCE


Prevalence is the number of people with CD or UC in a population at a given point in time or over a period of time (usually per year). The percentage of people in a population who have a disease is also usually determined; this is called the prevalence proportion.


There are different methods to measure the prevalence of a disease in a population. One method is to conduct a survey in a representative sample of the entire population. This will capture everyone with a diagnosed disease, including people who are not currently engaged in the health care system (for example, people in remission). This is particularly important for CD and UC, which have fluctuating courses of disease. In a population-based survey, a random sample of a population is asked if they have a given disease. The assumption is that people can accurately report if they have been diagnosed with a disease. This assumption has limitations because people can be confused with imprecise wording or may use different words to describe their disease.


Another method is to examine a database of health records. Every time a person visits a physician or is admitted to a hospital in Canada, the visit and the reason are recorded in electronic databases. These databases are made anonymous by removing all identifying patient information to ensure patient privacy and then made available to qualified researchers. In a database study, records are searched for people who match a set of criteria (such as, a physician visit due to IBD). This will capture people who have a disease as diagnosed by a physician and who seek health care. Because decades of medical history are contained within the databases, they should also capture people with fluctuating disease (who may go several years without any health care contacts for their disease). In Canada, with universal access to health care, electronic health database studies include the entire population of a province.


Canada is fortunate to have both survey and database studies of the prevalence of UC and CD. This report will focus on the Canadian-specific research, especially since we know that prevalence varies considerably by country. There will also be an international comparison to place the Canadian findings in context.


Canadian Community Health Survey


The Canadian Community Health Survey (CCHS) was conducted by Statistics Canada to provide cross-sectional estimates of health issues across Canada. Approximately 130,000 Canadians were surveyed in 2005 and asked a variety of health-related questions, including: “Do you suffer from a bowel disorder such as Crohn’s disease, ulcerative colitis, irritable bowel syndrome or bowel incontinence diagnosed by a health professional?” Based on the responses, the number of people and percentage of people in the population was estimated for each province. Results are presented in Figure 1 for CD and UC.


THE IMPACT OF INFLAMMATORY BOWEL DISEASE IN CANADA 29


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