Researchers Measure Rate of Crohn's and Colitis in Manitoba

Spring 2000

Researchers in Manitoba have completed the most extensive epidemiological study of inflammatory bowel disease (IBD) in North America and have established concrete statistics on the rate of Crohn's and colitis in that province.

Dr. Charles Bernstein, Associate Professor of Medicine and Director of the University of Manitoba IBD Clinical and Research Centre, and Dr. James Blanchard, Provincial Epidemiologist for Manitoba Health and Assistant Professor at the University of Manitoba, conducted Epidemiology of Crohn's Disease and Ulcerative Colitis in a Central Canadian Province: A Population-Based Study to assess the rate of IBD in Manitoba.

"It's the most extensive study in North America and one of only two population-based databases," Dr. Bernstein told The Journal. The study revealed that there are 14.6 new cases of Crohn's and 14.3 new cases of ulcerative colitis for every 100,000 people in Manitoba. The prevalence, or overall number of cases, are 198.5 per 100,000 for Crohn's and 169.7 per 100,000 for ulcerative colitis. Prevalence has increased since 1989, when the rates of Crohn's and ulcerative colitis were 152 and 127 respectively.

The number of IBD cases is significantly higher than those reported in the small number of other incidence studies that have been conducted. While this may suggest that Manitoba is harder hit by IBD than other areas, it is likely that the rate of IBD will be comparable across Canada. Preliminary data in Ontario and in a single-hospital database in Nova Scotia indicate similar rates as the Manitoba study.

"I don't think Manitoba is the single hotbed of Crohn's in Canada," Dr. Bernstein said, "it's just that we have the most up-to-date data to be reported."

Even so, the numbers are high enough to suggest the presence of some environmental factor(s) in Manitoba that contributes to the disease, researchers concluded in their report in the American Journal of Epidemiology (Vol. 149, No. 10, 1999).

Their next step will be a population-based case control study of possible risk factors, including various microbes, in IBD.

As part of that study, Drs. Bernstein and Blanchard will investigate the mpara tuberculosis (Mpara TB), the bacteria which has been the subject of much debate as a possible cause of Crohn's disease. The bacteria causes Johnes' disease in cattle, creating symptoms similar to Crohn's disease. Some researchers believe it is being passed on to humans through milk, contributing to or causing Crohn's disease. Recent news reports also suggest the bacteria may be getting into the water supply.

"We are pursuing this in our next population-based study," Dr. Bernstein said. "There are a lot of cattle in Canada with mpara TB. However, we may all have seen this bug and only few of us get IBD, so we are far from understanding a causal link."

Study Results
Incidence:
The overall incidence rates for Crohn's was 14.6 per 100,000. The highest incidence occurred in those between 20 and 29 years, followed by those between 30 and 39 years. There was steady decline in incidence rates as patients aged, with the lowest incidence occurring in people 60 years and older. The incidence of Crohn's was higher among women at 16.9 per 100,000 than among males at12.3 per 100,000.

For ulcerative colitis, the overall incidence rate was 14.3 per 100,000. The most common age group was the 20 to 29 year old group, followed by 30 to 39 years. Incidence rates decreased with age among females, although they did so more gradually than they did with Crohn's disease. Incidence rates among males remained fairly constant with increasing age.

Prevalence:
In 1994, 198.5 people per 100,000 had Crohn's disease. The peak incidence was in age groups 30 to 39 and 40 to 49. The prevalence of Crohn's was significantly higher among women than men.

The overall prevalence of ulcerative colitis in 1994 was 169.7 per 100,000, with peak prevalence at 40 to 49 years old.

How the data was collected
The main source of data for this study were the Manitoba Health insurance databases, which contains physicians records and hospitalization claims for Manitoba's 1.14 million residents. Researchers identified Manitoba residents with IBD by reviewing physician claims and hospital discharge information for the period April 1 1984 to March 31, 1995. To verify their identification methods, researchers polled more than 2,700 patients by questionnaire and conducted reviews of medical charts.

Individuals who were registered with Manitoba Health for at least two years between 1984 and 1995 were classified as having Crohn's or ulcerative colitis only if they had had at least five separate medical contacts with such a diagnosis. Individuals who were registered for less than two years during the study period were classified as having IBD if they had had at least three separate medical contacts.

Part of the discrepancy between these new statistics and other epidemiological studies is due to differences in the method of data collection. Other incidence studies have relied mainly on hospital data. This is not always a true reflection of IBD incidence because not all patients require hospitalization. Therefore, resulting incidence numbers would be an underestimation of incidence.

Editor's Note: Drs. Bernstein and Blanchard received funding from CCFC in 1998 and 1999 to study "The Requirements of Health Care Services by Patients with Inflammatory Bowel Disease in Manitoba: A Population-Based Study", which is related to the epidemiological study of incidence and prevalence.

Definitions
Prevalence refers to the total number of people who are affected by a disorder.
Incidence refers to the number of new cases diagnosed each year.
Both are tabulated per 100,000 population.

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