The prevalence of multiple sclerosis in the Australian-born population in five different regions of Australia has a strong correlation with latitude, the disease becoming increasingly prevalent with increasing south latitude. In this study, the prevalence in the migrant population from the UK and Ireland (UKI) in the different regions also showed a significant correlation with latitude, but this relationship was strongly influenced by the high prevalence in Hobart. Except for Hobart, the prevalence in migrants was considerably less than that in their countries of origin. The prevalence of multiple sclerosis among those migrating before the age of 15 years from the high-risk UKI to lower-risk Australia was not significantly different to that among those migrating at or after that age, and this finding was confirmed in a case-control study which demonstrated little association between age at migration and risk of developing multiple sclerosis. These findings suggest that the risk from environmental factors in multiple sclerosis may operate over a period of many years and not only in childhood and early adult life.
An epidemiological survey of multiple sclerosis (MS) in three Australian cities, Perth, Newcastle and Hobart, was undertaken with its prevalence day being the national census day on June 30, 1981, exactly twenty years after a previous survey of the same cities. The relationship between increasing prevalence and increasing south latitude found in the 1961 survey was confirmed in this present study. Prevalence rates had increased significantly over the twenty years between the studies. Over the same time period incidence rates had also increased in Newcastle and Hobart but had remained essentially stable in Perth although these changes were not significant. The rise in prevalence was due to a combination of factors of differing importance in each city. These factors included better case ascertainment, increased recognition of the less severely disabled patient, increased survival time and differential immigration of a population at a higher risk of developing MS than the indigenous population. Finally, analysis of MS prevalence rates amongst migrant populations in Perth and Hobart suggested that either the risk of acquisition of MS may extend over a wider age range than is generally accepted or that environmental factors prevalent in the former city have modified disease expression there.
Objectives (i) To determine the prevalence of multiple sclerosis (MS) in New South Wales and South Australia; (ii) to compare these prevalences with those in other areas of Australia and to determine the relationship between prevalence and latitude; (iii) to examine the relative contribution of genetic and environmental factors in the aetiology of the disease in Australia; and (iv) to ascertain whether there had been a change in the frequency of the disease since 1961. Results The crude prevalence of MS in New South Wales on prevalence day (National Census Day, 30 June 1981) was 37.2/100000 and the age‐standardised prevalence 36.6/100000. The female:male ratio was 2.3:1. The crude prevalence in South Australia was 29.4/100 000 and the age‐standardised prevalence 28.8/100000. The female:male ratio was 2.4:1. No Aborigines or Torres Strait Islanders with MS were identified. There was a significant increase in the prevalence with increasing south latitude in Australia, MS being about seven times more frequent in Hobart than in tropical Queensland, but no genetic differences were found in the surveyed population in different parts of Australia. A significant increase in the prevalence of MS occurred in most areas of Australia between 1961 and 1981, but this may not reflect a true increase in incidence. Conclusion The increasing prevalence with increasing south latitude cannot readily be explained by genetic susceptibility, and suggests that environmental factors are important for expression of the disease.
A previous study of the prevalence of multiple sclerosis (MS) in 1981 among immigrants from the United Kingdom and Ireland to Australia found that the prevalence for those with age at immigration (AAI) under 15 years of age did not differ from the older immigrants. We have reanalysed the original materials as well as census data for 1901–1981 for UKI and other high MS risk country immigrants. There was a highly significant trend in the prevalence rates of all Australians from New South Wales (NSW) to South Australia (SA) to Western Australia (WA) to Queensland (QLD). Rates by state among the Australian-born were almost identical to these, but there was no prevalence gradient for the UKI-born. The denominator population at risk of MS by AAI was calculated from special census tables of length of residence in Australia by age 0–79 in 1981 for UKI immigrants 1947–1981. The numerator was limited to the subset of 258 MS (Group II) also immigrating in 1947 and later, and age 0–79 in 1981. The absolute risk of MS for these migrants to the four states entering at age 0–14 was 22/100,000, significantly less than for all older age groups; age 15–39 immigrants had a risk of 54/100,000. Similar risk ratios for 0–14 versus 15–39 by state were 31 versus 61 (NSW), 29 versus 44 (QLD), 11 versus 50 (SA), 15 versus 51 (WA).
The data from an epidemiological study on multiple sclerosis in Australia have been analysed to determine the relation between the prevalence of the disease and educational level, and the association between level of disability and employment status. There was a significantly higher frequency of multiple sclerosis in those who left school at an older age and achieved a higher educational level. The explanation of this finding remains speculative and may be related to genetic or environmental factors. The study confirmed the recognised association between moderate-severe disability and divorce-separation and lower rates of employment.
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