The relation between type of farming and prevalence of Parkinson's disease among agricultural workers in five French districts.

Retrospective assessment of pesticide exposure is complex; however, patterns of pesticide use strongly depend on farming type, which is easier to assess than pesticide exposure. Our aim was to estimate Parkinson's disease (PD) prevalence in five French districts in 2007 among affiliates of Mutualité Sociale Agricole (MSA) and to investigate the relation between PD prevalence and farming type. We identified PD cases from administrative files as persons who used levodopa and/or benefited from free health care for PD. Densities of 16 farming types were defined at the canton of residence level (1988 French agricultural census). We used logistic regression to study the relation between PD prevalence and density of farming types and a semi-Bayes approach to deal with correlated exposures. We identified 1,659 PD cases, yielding an age- and sex-standardized PD prevalence of 3.01/1,000. Prevalence increased with age and was higher in men than women. We found a higher PD prevalence among affiliates living in cantons characterized by a higher density of farms specialized in fruits and permanent crops (multivariable semi-Bayes model: OR(4+5 vs 1+2+3 quintiles) = 1.21, 95% CI = 1.08-1.36; test for trend, P = 0.035). In France, farms specialized in fruits and permanent crops rank first in terms of insecticide use per hectare. Our findings are consistent with studies reporting an association between PD and insecticide use and show that workers in farms specialized in fruits or permanent crops may be an occupational group at higher PD risk.