Numerous epidemiologic studies have attempted to detect occupations at high risk for developing PD. Fall et al. (65) performed an occupation case-control study and found an increased risk of PD in carpenters (OR=3.9), cabinet-makers (OR = 11), and cleaners (OR = 6.7), compared to a population-based control group. Tanner et al. (66) performed a case-control study (nonpopulation-based) of occupational exposures and PD in People's Republic of China and found that occupations involving industrial chemical plants (OR=2.39), printing plants (OR=2.40), and quarries (OR=4.50) were associated with a higher risk of PD. A population-based survey of PD in British Columbia found an association between PD and working in an orchard (adjusted OR=2.30) or planer mill (adjusted OR=4.97) (67). They hypothesized that industrial chemicals, including pesticides and herbicides, could be etiologic agents. Another nonpopulation-based case-control study in the same region found that occupational categories, including forestry, logging, mining, and oil/gas field work, had the highest odds ratios (3.79) (68). Although referral bias of affected subjects may have influenced the results, the number of subjects studied (n = 414) was substantial. Another nonpopulation-based case-control study in the Emilia-Romagna region of Italy found that occupational exposure to "industrial chemicals" was a risk factor for PD (OR = 2.13) (69). Among industrial chemicals, only organic solvents were identified as a risk factor (OR=2.78). Limitations of this study include lack of specific information regarding occupations, small sample size, and subject selection bias.
Occupational exposure to magnetic fields may be a risk factor for PD (70). A death certificate (population-based) case-control study in Colorado, U.S.A. utilizing a tiered exposure matrix found an adjusted odds ratio of 1.76 for PD subjects exposed to magnetic fields. Occupations included in this study were electronic technicians and engineers, repairers of electronic equipment, telephone and telephone line installers and repairers, electric power installers and repairers, supervisors of electricians and power transmission installers, power plant operators, motion picture projectionists, broadcast equipment operators, and electricians (70). Another study of electrical workers in a similar group of occupations found a nonsignificant, elevated odds ratio of 1.1 for PD compared to controls, but the study lacked power (71).
Several studies have investigated the association between residential exposures to industrial toxins and PD. Using standard industrial code classifications, Rybicki et al. (28) found that residential exposure to industrial chemicals, iron, and paper were significantly associated with the development of PD. The counties in Michigan, U.S.A. with the highest concentration of these industries had the greatest death rate from PD, suggesting that these individuals resided in an environmentally high-risk region. In a case-control study in People's Republic of China, subjects living near a rubber plant appeared to have a higher risk of PD; however, no specific data on those working in the plant were provided (72).
Most epidemiologic studies have focused on categories of exposure and not on specific occupations. A few occupations warrant specific attention, given the type of chemical exposures or the amount of data supporting these occupations in the etiology of PD.
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