Amyotrophic lateral sclerosis, rural environment and agricultural work in the Local Health District of Ferrara, Italy, in the years 1964-1998

Previous epidemiological surveys, both analytic and descriptive, in the Local Health District (LHD) of Ferrara, northern Italy, have indicated that rural residence and agricultural work might constitute risk factors for Amyotrophic Lateral Sclerosis (ALS). The present investigation is a demographic survey in the LHD of Ferrara in the years 1964-1998 which aimed to verify whether the level of urbanization and agricultural activities might influence the risk of ALS. Based on the data obtained in a recent incidence study in the LHD of Ferrara which reported a mean annual crude incidence rate of ALS in the years 1964-1998 of 1.63 per 100,000 population (95% CI 1.31-2.00), it was possible to compare the number of observed ALS cases and the number of expected ALS cases according to the level of urbanization and usual occupation on the basis of the residential and occupational pattern identified in the population of the LHD of Ferrara in the study period under the assumption of a homogeneous distribution of ALS. The present survey identified four different levels of urbanization in the LHD of Ferrara in the study period and for none of them was a difference between the number of observed and expected ALS cases found. Also in the most rural of the four identified levels of urbanization (small villages with an average population in the study period lower than 1,000 inhabitants and scattered houses in the countryside) no difference was found between observed and expected number of ALS cases (observed ALS cases 16, 95% Poisson CI 9.1-25.9, expected ALS cases 18.3). Based on the occupational pattern identified in the population of the LHD of Ferrara in the study period the number of incident cases of ALS whose usual occupation was in agricultural work exceeded the expected number (observed ALS cases 22, 95% Poisson CI 13.8-32.3, expected ALS cases 6.0). The present findings indicate that rural residence itself does not influence the risk of ALS while agricultural activities could influence the risk of ALS, with occupational exposure to agricultural chemicals playing a possible role.