Multiple Sclerosis incidence rate in southern Iran: A Bayesian epidemiological study

Abstract Background: Multiple Sclerosis (MS) remains to be a public health challenge, due to its unknown biological mechanism and clinical impact on young people. The prevalence of this disease in Iran is reported to be 5.3 to 74.28 per 100000 cases. Due to high prevalence of this disease in Fars province, this study aimed to assess the distribution of MS in this region in southern Iran by evaluating its covariates.Method: Data from 5,468 patients diagnosed with MS were collected, according to the McDonald’s criteria, which was reported by the MS Society of Fars from 1991 until 2016. Bayesian spatio-temporal models was also used to describe MS incidence in Fars province. We also investigated the association between overall MS incidence rate and the overall percentage of vitamin D intake, smokers in the population as well as the overall percentage of people with normal BMI as well as alcohol consumption in a population from 1991 until 2016 by Besag, York and Mollie's (BYM) model.Results: County-level crude incidence rates ranged from 0.22 to 11.31 cases per 100,000 population. The highest relative risk was estimated at 1.8 in the city of Shiraz, the capital of Fars province while the lowest relative risk was estimated at 0.11 in Zarindasht County in southern Fars. The percentages of vitamin D3 intake was significantly associated with the incidence of MS. Although 1% increase in Vitamin D3 intake is associated with 2% decrease in the risk of MS, 1% increase in smoking is associated with 16% increase in the risk of MS, respectively.Conclusion: Spatial analysis of MS showed low incidence rate of this disease in the south and south east of Fars province, which is due to the effect of different covariates. As suggested by previous studies, vitamin D and smoking among all covaiates might be associated with high incidence of MS.