Pharmacoepidemiology and the Australian regional prevalence of multiple sclerosis

Background: Over some 50 years, field surveys have shown that the prevalence of multiple sclerosis (MS) increases with increasing distance from the equator in both the northern and the southern hemispheres. Such a latitudinal gradient has been found in field surveys of MS prevalence carried out at different times in various local regions of Australia. Objective: The objective of this paper is to use a pharmacoepidemiological approach to obtain whole of population estimates of the prevalence of MS in the various Australian states and territories from the use of MS disease-modifying drugs used to treat relapsing-remitting MS (RRMS). Methods: We analysed the dispensed use of subsidised RRMS drugs by jurisdiction. Results: In the 2005-2008 period, the calculated mean treated RRMS prevalence in Australia ranged from 7.5 per 100,000 in the far north to 53.2 per 100,000 in the extreme south and was linearly related to increasing southerly latitude. Public domain Australian data suggested that multiplying this prevalence by a factor of 2.2 (to account for untreated RRMS and other types of MS) may provide a measure of the prevalence of all varieties of the disease. Conclusion: These findings provide contemporary and more comprehensive evidence for the gradient of MS prevalence with latitude in Australia than has previously been available.