PM exposure as a risk factor for multiple sclerosis. An ecological study with a Bayesian mapping approach.

Some environmental factors are associated with an increased risk of multiple sclerosis (MS). Air pollution could be a main one. This study was conducted to investigate the association of particulate matter 2.5 (PM) concentrations with MS prevalence in the province of Pavia, Italy. The overall MS prevalence in the province of Pavia is 169.4 per 100,000 inhabitants. Spatial ground-level PM gridded data were analysed, by municipality, for the period 2010-2016. Municipalities were grouped by tertiles according to PM concentration. Ecological regression and Bayesian statistics were used to analyse the association between PM concentrations, degree of urbanization, deprivation index and MS risk. MS risk was higher among persons living in areas with an average winter PM concentration above the European annual limit value (25 μg/m). The Bayesian map revealed sizeable MS high-risk clusters. The study found a relationship between low MS risk and lower PM levels, strengthening the suggestion that air pollution may be one of the environmental risk factors for MS.