An ecological study of industry in a high-risk region of multiple sclerosis.

The county of Värmland, Sweden, has shown a high frequency of multiple sclerosis in several investigations. It has been presented in three studies; a period prevalence study in 1925-1934, a mortality study during 1952-1992 and a prevalence investigation in 2002. The aim of this study was to investigate the pattern of industry in this high-risk area for multiple sclerosis. The three investigations were correlated with industry in 1913 and in the 1950s, all analyzed by the Kruskall-Wallis test. Select industries from wood-pulp, paper and iron/mechanical sectors were tested also in whole Sweden. The Spearman rank correlation was used for these data and forestry data in Värmland. In Värmland, industrial data from 1913 revealed that large sawmills were associated with the period prevalence in 1925-1934 and there was a possible correlation with the prevalence for 2002. Wood-pulp factories showed a possible association with the prevalence 1925-1934 and the mortality 1952-1992. Some industries in the 1950s were correlated with the prevalence 2002. Wood and paper industries in Sweden 1913 showed an association with the MS mortality 1952-1992. In summary, data on MS prevalence in Värmland and mortality both in Värmland and all Sweden from the past 100 years suggest an association with wood-related industries in 1913 and in the 1950s, whereas no consistent association was found for other industries.