Prevalence of multiple sclerosis among immigrants in Norway.

BACKGROUND Multiple sclerosis (MS) prevalence is unevenly distributed worldwide. Immigration to Norway from countries with a lower MS prevalence is increasing. The aim of this study was to investigate MS prevalence in different immigrant populations in Norway and evaluate the effect of migrating from low- to high-risk regions of MS. METHOD First- and second-generation immigrants from the largest immigrant populations were identified from the 2012 Norwegian prevalence study. Prevalence of MS in different ethnic groups was compared using the standardized prevalence ratio (SPR). RESULTS European and North-American immigrants had the highest prevalence of MS, whereas African and Asian immigrants had the lowest. The prevalence of first-generation Iranian immigrants was not significantly different from the total Norwegian population (SPR 0.70, 95% CI: 0.46-1.03). Second-generation immigrants from Pakistan (SPR 1.62, 95% CI: 0.88-2.76) had a strong increase in prevalence compared to the first generation (SPR 0.13, 95% CI: 0.05-0.28). CONCLUSION MS prevalence among immigrants in Norway in general reflects the uneven distribution worldwide. The sharp increase in prevalence in immigrants seen in one generation suggests strong environmental factors affecting the MS risk in Norway.