The epidemiology of Crohn's disease.

Individual studies on the epidemiology of Crohn's disease have been conducted, mostly confined to one city, county or region of a country. Only three countries have conducted national surveys on the prevalence and incidence of Crohn's disease. These are Japan, Slovakia and Yugoslavia. There is insufficient data to develop a complete picture of the global prevalence or incidence of Crohn's disease.

I have gathered together the available studies into one table. See the page "Crohn's disease epidemiology statistics" to see the table itself. It contains a large number of links, one for each of the studies from which the data are taken, and links that explain the content of each data column in the table.

Although the global picture is incomplete, there is still much important information to be gathered from the studies presented. I have presented this information below.

Crohn's disease is caused by something in the environment.

Several of the studies mentioned study ethnic subgroups of populations. In these studies, people whose country of origin has a low or zero prevalence of Crohn's disease have a much higher prevalence of the disease when they migrate to a country that has high prevalence of the disease. For example, Moroccans living in Belgium, West Indians living in England and Asians living in England are as much at risk of developing the disease as the indigenous populations of those countries. This provides strong evidence that a factor in the environment is involved in causing Crohn's disease.

Further evidence that an environmental factor is involved is provided by studies that show that the pattern of relapse of Crohn's disease changes through the year. In this following study, it was found that there was a higher rate of relapse in the autumn and winter months. See the reference "Seasonal change in the exacerbations of Crohn's disease". Could this perhaps be related to seasonal variation of Mycobacterium paratuberculosis in retail milk supplies?

Geographic correlation between BJD (Bovine Johne's Disease) and Crohn's disease.

If Crohn's disease is caused by Mycobacterium paratuberculosis, then it is reasonable to assume that there should be a geographic correlation between areas with a high prevalence of BJD and areas with a high prevalence of Crohn's disease. However, there are several factors to be taken into account

• Infection from contaminated food. One of the potential routes for infection with Mycobacterium paratuberculosis is through contaminated beef and dairy products. The food production and transport industries have changed radically in recent decades, and people often consume food that comes from an area which is geographically distant from where they live, e.g. people in California eat food produced in the Great Lakes region.
• Infection from contaminated water supplies. In contrast to the food situation, water is seldom transported long distances for consumption. Instead, it is both treated and consumed locally.

Until 1996, no research groups had conducted a comparison of the prevalence of BJD and Crohn's disease on a geographical basis. However, in 1996, Tamboli published the results of just such a comparison in the Canadian Journal of Gastroenterology. He found that "There is considerable overlap of regions with high prevalences of paratuberculosis and Crohn's Disease. This finding adds support to the implication of M paratuberculosis in the etiology of Crohn's Disease".

Crohn's disease is on the rise throughout the world.

Of the studies which looked for a change in the incidence of Crohn's disease, almost all found a marked increase in the annual incidence of the disease. Annual growth rates between 2 and 14 per cent have been recorded. In some cases these growth trends have been maintained for periods of up to fifty years. For example, in Cardiff, Wales, the annual incidence of Crohn's disease grew from 0.18 per 100,000 in 1934 to 8.3 per 100,000 in 1985, a forty six fold increase in 51 years. One possible explanation for this that there is a subset of the population that is genetically susceptible to Crohn's disease. In populations across the world, the disease is expanding in this subset of people at a high and increasing rate. Only when this subset of people is saturated with the disease does the incidence rate start to fall again, since most of the people that can have the disease actually do have it. If so, Cardiff would appear to be to be in the position of having reached that saturated stage. After 1985, the incidence of Crohn's disease in Cardiff stopped increasing..

Crohn's disease is increasing in Children.

Crohn's disease is on the rise in children. One study, in South Glamorgan, Wales, found that the annual incidence of Crohn's disease in children was increasing by over nine per cent per year. Another study in southwest Sweden concluded that the incidence of Crohn's disease among children had risen. To get an idea of the effects of Crohn's disease on children, see the reference "Pediatric Crohn's disease".

The North-South Gradient is lessening.

In the past, the evidence of high prevalence rates in northern countries and low prevalence rates in southern countries led researchers to conclude that the incidence of the disease followed a North-South Gradient. However, there is evidence, from studies in Spain, Greece and Portugal that Crohn's disease is on the increase in southern countries. The reasons for this are unknown. Could it be that the environmental agent that causes Crohn's disease is spreading in those countries, or that an increased of amount of travel in todays world results in people from those countries being exposed to an environmental agent when abroad?

Crohn's disease is appearing outside Europe and North America.

Historically, Crohn's disease has been pictured in the past as a disease that affects mostly white populations. As has been shown above, non-white migrants to Europe and North America are at a much greater risk of developing the disease than they are in their country of origin. Also, the disease is beginning to make itself known in populations where it has never been seen before, such as in Chinese people in Hong Kong, Chinese people in Singapore, and Arab people in Kuwait. Again, could this be a result of increased travel to high-prevalence countries? In Japan, the disease has been on the rise for many years. A recent study in Japan found a statistical correlation between the growth in incidence of Crohn's disease and the increasing consumption of animal proteins, with the highest correlation figure being associated with increased consumption of milk.

Source: http://archive.crohn.ie/epidem.htm
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