Geographic clustering & Northern Latitude disease.
Increased rates of precipitation. Increased pesticide use. Increased autoimmune disease.
Temperate cereal growing regions, with higher rainfall than arid regions, tend to show higher rates of autoimmune disease and other gut related diseases.
Do these regions have more pesticide residues which end up in the drinking water and food of local populations, with the result that these populations act as lead indicators for pesticide related diseases? Is this clearly expressed in geographic cluster regions for autoimmune disease and disorders of the gut - such as celiac, IBS (Irritable Bowel) and Crohn's disease?
A 2009 study asked the question: 'What is the common denominator between Canterbury in New Zealand, Manitoba in Canada, Aberdeen in Scotland, Amiens in France, Maastricht in Netherlands, and Minnesota in US? Unlocking this strange relationship would subsequently unlock the mystery of Crohn’s etiology, still speculated upon 75 years after its baptism.' 
The study authors couldn't understand why the incidence of Crohn's disease spiked at particular North-South latitudes.
These regions are large cereal (and oilseed) producers. Many even have local cereal research institutions or agricultural universities. Most cereal based food products for the local population will be sourced locally.
- Canterbury in NZ is the primary cereal growing region for NZ.
- Aberdeen in Scotland - oat and wheat growing region of the UK. (England and Wales also have fluctuating/high levels - perhaps years where local harvests are bountiful causes spikes).
- Manitoba: Canola and wheat occupy over 50% of harvested crops. Precipitation is higher in Alberta and Manitoba than Saskatchewan. The first two have higher Crohn's incidence.
- Cereals are the primary crops of Picardie, France, of which the capital is Amiens.
- Maastrich: cereal grower, primarily wheat and barley.
- Minnesota: (close to the great lakes) primary crops are soft white wheat and canola. The prevalence of Crohn's disease is lower in the southern states of America.
However these primarily Northern regions have slightly higher rates of precipitation than dryer/arid temperate zones that are also heavy cereal producers (eg. Southern France, the wheat belt of the USA).
Why might these regions have a higher frequency of pesticide application?
Many pests (particularly insect and fungal pests) tend to be more abundant in regions with higher annual precipitation. Dryer regions with lower moisture levels simply have less weed, insect and fungal growth. Additionally, 'higher precipitation leads to a greater potential for pesticides to enter surface waters through surface runoff, leaching to groundwater and soil erosion. Increased rainfall can also cause pest outbreaks, increasing the need for pesticide application'. 
Farmers in these regions may be more likely to desiccate wheat or barley with diquat (Reglone - a cell membrane destroyer) in order to bring their crops to maturity earlier, and/or glyphosate based herbicides, to reduce weed matter. Farmers in dryer temperate zones don't have such pest growth. Desiccation has been used for over 20 years. Usually, farmers would prefer not to use glyphosate to desiccate, or 'dry down' the crop. But due to inclement weather, heavy moisture and fungal disease and faster weed growth, these and many other chemicals can be commonly used. The following can all be used post-emergent on the wheat leaf in New Zealand and would likely apply to the US. (Europe may have more stringent standards and not use some of these chemicals). :
Fungicides: Strobiluron (pyraclostrobin, azoxystrobin); azole (prothioconazole); carboxamide (isopyrazam); anilide (carboxin); sulfur (thiram).
Herbicides for weed reduction: Organophosphates (diazinon or glyphosate based mixes); sulfonylureas (Chlorsulfuron, tribenuron-methyl, thifensulfuronmethyl, iodosulfuron-methyl-sodium, mesosulfuron ); Urea herbicides (isoproturon); chlorophenoxy herbicides (dicamba); phenoxycarboxcylic acids (2,4-D, mecoprop, MCPA, MCPB); Pyridine carboxylic acid (fluroxypyr) FOPs (Fenoxaprop-P-ethyl, clodinafop); bleachers (diflufenican) and chelating herbicides such as bipyridyl and unknown mode of action: flamprop-M-isopropyl
Growth regulants: (chlormequat-chloride, trinexapac-ethyl)
Insecticides: diazinon (banned EU - in NZ Diazinon is used on 50-60% of cereals ), chlorpyrifos, sulfoxaflor.
The above listed regional populations may be more exposed to pesticides (than people living in dryer Southern regions) due to residues in drinking water and local bakeries purchasing locally desiccated wheat/oats etc. I postulate that the higher incidence of Crohn's in these cities, is a case of the classic canary in the coal mine. It may evolve from from increased pesticide exposure, after all the significant common denominator is that these are cereal growing economies in higher rainfall regions. Increased pesticide exposure may be reflected in the growing incidence of rheumatoid arthritis, autism and multiple sclerosis in these regions. For example the Canterbury region of NZ has the highest incidence of celiac, ankylosing spondylitis, Wegener’s Granulomatosis, Irritable bowel (IBS) and Crohn's disease in NZ.
Glyphosate is rarely tested in groundwater or drinking water. Atrazine may be tested, but not glyphosate (it is a separate test). None of the above listed pesticides are assessed for their effect on the gastric, immune and endocrine systems. Research data correlates vitamin D deficiency in Northern latitudes and questions it's contribution to infant malformations, Multiple Sclerosis etc. Should governments question the increased Roundup residues in drinking water, wheat, cereals and GMOs, and ask whether 'glyphosate’s interference with CYP proteins may play a role in disrupting vitamin D3 activation in the liver'.  It is possible there is a cumulative impact of insecticides, herbicides and fungicides in these regions that contibute to higher disease rates.
'When an environmental agent alters the function of the microbiota, the result can be disease'. 
Communities living in even more extreme Northern latitudes - Eg. Canada's Inuit, on traditional diets (that would not include cereals and GMOs treated with glyphosate, and away from groundwater contaminated by pesticide runoff) do not have the same rates of multiple sclerosis and malformations.
Are these regions presenting as the centre of a 'pesticide related illness' storm?
If you live in these regions, consider requesting:
- Local and national governments to regularly assess glyphosate (Roundup) and other pesticides (for example diquat and chlorpyrifos) in drinking water, groundwater and locally produced foods including cereal products.
- Research to increase knowledge on the environmental origins of disease
- Governments fund independent research into pesticides effect on the endocrine, immune and gastric systems.
The first duty of government is to afford protection to it's citizens.
 Incidence and prevalence of Crohn’s disease and its etiological influences. Economou M., Zambeli, E., Michopoulos S. ANNALS OF GASTROENTEROLOGY 2009, 22(3):158-167
 PRESENCE AND LEVELS OF PRIORITY PESTICIDES IN SELECTED CANADIAN AQUATIC ECOSYSTEMS. Water Science and Technology Directorate. Environment Canada. March 2011. Cat. No.: En14-40/2011E-PDF. ISBN 978-1-100-18386-2
The Autoimmune Epidemic: Bodies Gone Haywire in a World Out of Balance. Excerpt by D. Jackson Nakazawa.
 Gut Reaction: Environmental Effects on the Human Microbiota. M.L. Phillips. Environ Health Perspect. May 2009; 117(5): A198–A205.