Rheumatoid arthritis and spondyloarthropathies: geographical variations in prevalence in France.

To determine geographical variation in the prevalence of rheumatoid arthritis (RA) and spondyloarthropathies (SpA) in France. The survey sample was drawn from 7 areas of France. Households were randomly selected using the national telephone directory, and an individual within each household was randomly chosen by the next-birthday method. All cases of suspected RA and SpA were confirmed by the patient's rheumatologist or by clinical examination. Standardized estimates of prevalence were compared between regions and groups of regions. In total 15,219 anonymous telephone numbers were selected. An average response rate of 64% led to a total of 9395 respondents included in the study. The highest regional rates of RA were observed in the south (range 0.59-0.66%), and the lowest in the north (range 0.14-0.24%), with a national rate of 0.31% (95% CI 0.18-0.48%). Regional heterogeneity was observed for SpA, with the highest rates in Bretagne (0.47%) and the Sud-Est (0.53%) and a national rate of 0.30% (95% CI 0.17-0.46%). This study is the largest of its kind conducted in France. It shows inter-regional variations, mainly in RA, with a higher prevalence in the south of the country. The many potential reasons for the heterogeneity observed, including genetic and environmental factors, warrant further research.