Comparing questionnaire-based methods to assess occupational silica exposure

Background: Epidemiologic assessment of occupational exposure to silica is typically limited to long-term work in the dusty trades, primarily in jobs held by men. We compared alternative questionnaire-based methods to assess silica exposure in a recent case-control study of 265 patients with systemic lupus erythematosus (mostly women) and 355 controls randomly selected from state driver's license registries and frequency-matched by age and sex. Methods: In-person interviews included a job history (all jobs held at least 12 months) and checklist of silica-related jobs and tasks (work of at least 2 weeks). Three industrial hygienists reviewed job descriptions without knowing case-control status. Potential high- or moderate-intensity exposures were confirmed or revised based on follow-up telephone interviews. Results: In the full assessment including all work of at least 2 weeks, 9% of cases and 4% of controls were classified as medium or high silica exposure (odds ratio of disease = 2.9; 95% confidence interval = 1.3-6.4). In contrast, only 4% of cases and 9% of controls were identified by the standardized code groups index as having worked in silica-related industries or occupations for at least 12 months, providing a much lower risk estimate for disease (0.4; 0.2-0.9). Conclusions: Specific task-based questions must be included to assess the full potential of occupational silica exposure. These findings highlight the limitations of using standardized code groups to define exposure or to select jobs for industrial hygienist review.