Regional variations in the prevalence of multiple sclerosis in French farmers

Background: Studies on the prevalence of multiple sclerosis have been carried out worldwide, showing a heterogeneous distribution between countries and even between the different regions of the same country. Methods: We estimated the regional and national prevalence of multiple sclerosis in France on 1 January 2003, based on the computerised database of the national farmer health insurance system ("Mutualite Sociale Agricole"). Results: There were 2667 cases of multiple sclerosis registered on the prevalence date, out of 4 098 477 affiliates. After standardisation on age, estimates for the national prevalence of multiple sclerosis in French farmers were 65.0 per 100 000 inhabitants (95% confidence interval 62.5 to 67.5), 41.9 per 100 000 in men (39.1 to 44.7) and 96.3 per 100 000 in women (92.0 to 100.6). The prevalence of multiple sclerosis was significantly higher in the north eastern regions (approximately 100 per 100 000 inhabitants) compared with the south western regions (around 50 per 100 000 inhabitants). Conclusion: Our study is the first to evaluate the overall prevalence of multiple sclerosis in France and its 22 regions using the same methodology. Our results may be generalised to the whole French population as there is no convincing evidence of an increased or decreased susceptibility to multiple sclerosis among farmers or persons living in the countryside. This places France among the countries of medium to high prevalence. Confirming the uneven distribution of multiple sclerosis that correlates with latitude, raises once more the question of the role of genetic and environmental factors in the susceptibility to multiple sclerosis.