Background: Aim of this study was to assess whether previous employment in certain occupations could be a risk factor for Amyotrophic Lateral Sclerosis (ALS) incidence. This topic has been explored by several studies, but no risk factor has been firmly identified. Methods: The study population consisted of all subjects over 30 years old resident in Turin in 1996 who worked or were unemployed at 1991 Italian census (n = 284 406), followed up for ALS occurrence from 1996 to 2014. The risk of ALS was estimated in relation to the occupation held in 1991, using the Italian classification of occupations at the greatest detail. The association between occupations and ALS risk was estimated through Huber-White sandwich multivariate Poisson regression models adjusted for age, gender, education and marital status. Results: During the follow-up, 208 subjects developed ALS. ALS risk was significantly associated with previous employment as bank teller (IRR = 7.33), general practitioner (IRR = 4.61) and sales representative (IRR = 3.06). Categorizing all occupations as exposed or unexposed to direct contact with general public, it was found that previous employment in this group of occupations increased significantly ALS risk (IRR = 1.51), mainly driven by occupations in direct contact with customers (IRR = 1.79). Conclusions: The study results indicate that ALS risk may be increased by previous employment in occupations implying direct contact with the general public, in particular customers. A possible explanation of this finding, partly supported by the literature, is that workers in contact with the public could be more exposed to certain infections, which would increase their ALS risk.

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