Inflammatory Bowel Disease Is as Canadian as the Mounties

WINNIPEG, Manitoba, Aug. 24 -- Canadians from coast to coast are remarkably prone to inflammatory bowel disease, possibly the result of a climate that discourages bacterial activity and promotes sterile conditions in childhood.

About 0.5% of Canadians have inflammatory bowel disease, which means ulcerative colitis and Crohn's disease together strike about one in 350 persons, according to a study published in the July issue of the American Journal of Gastroenterology.

"Canada has the highest incidence and prevalence of Crohn's disease yet reported," wrote Charles N. Bernstein, M.D., of the University of Manitoba here, and colleagues.

The researchers found that ulcerative colitis, the inflammatory bowel disease that affects only the large intestine, strikes an average of 194 of every 100,000 Canadians, with 11.8 new cases per 100,000 each year.

Crohn's disease, which affects the large and small intestines, is even more common in Canada and affects about 234 per 100,000 people, with an incidence of 13.4 per 100,000 each year.

By comparison, ulcerative colitis prevalence is 58 to157 per 100,000 in Northern Europe and about 167 per 100,000 for an area of Minnesota. Crohn's disease prevalence ranges from 27 to 48 per 100,000 in Northern Europe to 144 per 100,000 in an area of Minnesota.

Some Third World nations and areas in tropical latitudes have still lower rates.

Although the reasons for these differences remain unclear, the hygiene hypothesis may help explain the distribution in Canada, said Richard Fedorak, M.D., of the University of Alberta in Edmonton, a co-author.

"If you live in an environment that's too clean or too sterile as a child your intestines are not exposed to bacteria of the same types and numbers you would be exposed to in a tropical area," he said. which is especially true for Canada because much of the country has cold winters with little bacterial activity in the soil.

Then if the genetic triggers are present, "your intestine is not able to tolerate bacteria as you get older and starts to destroy itself," he added.

Supporting this speculation, the researchers discovered differences among provinces:

• Nova Scotia in the Maritimes consistently had the highest rates of ulcerative colitis (19.2 incidence and 247.9 prevalence per 100,000) and Crohn's disease (20.2 incidence and 318.5 per 100,000),
• Following closely is Alberta, with ulcerative colitis incidence of 11.0 and prevalence of 185.0 per 100,000 and Crohn's disease incidence of 16.5 and prevalence of 283.0 per 100,000, and
• Manitoba had likewise high rates of ulcerative colitis (15.4 incidence and 248.6 prevalence per 100,000) and Crohn's disease (15.4 incidence and 271.4 prevalence per 100,000);
• Whereas British Columbia, on the west coast, consistently had much lower rates of both ulcerative colitis (9.9 incidence and 162.1 prevalence per 100,000) and Crohn's disease (8.8 incidence and 160.7 prevalence per 100,000).

British Columbia proved to be an outlier, particularly for Crohn's disease perhaps because of its milder winters, more precipitation, and "because its population ethnic make-up is somewhat different from the rest of Canada," the researchers wrote.

Much of British Columbia's immigration in the past 20 years has been from Asia, they said. "Asians are known to have less [inflammatory bowel disease] than Caucasians," perhaps because of genetics, less sterile conditions during childhood, or other environmental factors.

Males and females generally had similar rates of ulcerative colitis though significantly more females had Crohn's disease (1.31 ratio, 95% CI 1.23-1.40). Notably, though, the prevalence of Crohn's disease was significantly greater in boys than girls (prevalence 49.6 versus 43.8 per 100,000, P=0.0001).

After adjusting for age, gender, and province, the prevalence of ulcerative colitis and Crohn's disease were slightly more common in urban areas (urban-to-rural ratio 1.13 (P=0.01) and 1.05 (P-value not significant), respectively).

The researchers used government health system databases from five of the 10 Canadian provinces (British Columbia, Alberta, Saskatchewan, Manitoba, and Nova Scotia) to determine the number of individuals who received health care, whether hospital- or outpatient clinic-based, for either type of inflammatory bowel disease.

They defined a case as an individual who had at least five "health-care contacts" or three or more contacts if in the health system for less than two years. The researchers said this highly specific definition may tend to underestimate the prevalence and incidence of this condition.

However, this method is more accurate than looking at a small sample then extrapolating as has previously been done, Dr. Fedorak said.