Pesticide exposure and risk of Parkinson's disease-a population-based case-control study evaluating the potential for recall bias

Objective The aim of this study was to investigate whether pesticide exposure was associated with Parkinson's disease in a population-based case-control study in British Columbia, Canada. Methods Patients reimbursed for anti-parkinsonian agents were identified and screened for eligibility as cases. Controls were selected from the universal health insurance database, frequency-matched to the case sample by birth year, gender, and geographic region. A total of 403 cases and 405 controls were interviewed about their job, medical and personal habits histories, and beliefs about disease risk factors. Among those reporting pesticide exposure, an occupational hygiene review selected participants exposed beyond background (ie, above the level expected in the general population). Unconditional logistic regression was used to estimate associations for different pesticide categories. Results Of the cases, 74 (18%) self-reported pesticide exposure and 37 (9%) were judged to be exposed beyond background. Self-reported exposure was associated with increased risk [odds ratio (OR) 1.76, 95% confidence interval (95% CI) 1.15-2.70], however the risk estimate was reduced following the hygiene review when restricted to those considered exposed (OR 1.51, 95% CI 0.85-2.69). When agricultural work was added to the model, the risk for hygiene-reviewed pesticide exposure was not elevated (OR 0.83, 95% CI 0.43-1.61), but agricultural work was (OR 2.47, 95% CI 1.18-5.15). More than twice as many cases as controls thought chemicals cause Parkinson's disease. Discussion This study provides little support for pesticide exposure as a cause of Parkinson's disease. The observed pattern of step-wise decreases in risk estimates might indicate differential recall by case status. The relationship to agricultural jobs suggests that farming exposures - other than pesticides - should be considered as risk factors for Parkinson's disease.