Trends in the epidemiology of multiple sclerosis in Greater Hobart, Tasmania: 1951 to 2009

Background Hobart, Tasmania has been the site of two major studies of multiple sclerosis (MS) frequency, in 1951-1961 and 1971-1981. Since then, there have been no studies of MS frequency in Hobart. Methods Using a prevalent cohort of 226 cases in 2001 and 265 in 2009, the authors undertook a two-stage survey of MS frequency in Hobart. Combined with the published data from the two preceding studies, the authors conducted a time-trend analysis of MS epidemiology over 1951-2009. Results The age-standardised prevalence in 2001 was 96.6/100 000, and 99.6/100 000 in 2009, a significant increase from the 1961 prevalence of 32.5/100 000 (p<0.001). Female prevalence increased over each time point; male prevalence increased between 1961 and 2001 but was unchanged thereafter. Incidence over 2001-2009 was 3.7/100 000, significantly increased from the 1951-1961 incidence of 2.2/100 000 (p=0.004), though the majority of this was between 1951-1961 and 1971-1981. Mortality fell by half from 2.4/100 000 in 1951-1959 to 1.0/100 000 in 2001-2009-this decreased mortality and an older cohort contribute to the increase in prevalence. Neither prevalence (p=0.48) nor incidence (p=0.18) sex ratios changed significantly between 1951 and 2009. Conclusions Between 1951 and 2009, the age-standardised prevalence of MS in Hobart increased threefold, and the incidence nearly doubled. Part of the increase in prevalence was due to an increased longevity, decreased mortality and increased incidence. Differences in patterns by birthplace may be explained by the Australian assisted-migration programme of 1945-1981. These data do not demonstrate the strong and significant changes in sex ratio observed elsewhere.