A case-control study (8,740 cases; 83,338 controls) was done to evaluate the association between potential occupational exposure to silica and risk of tuberculosis (TB) mortality, using the National Occupational Mortality Surveillance database for 1983-1992. Potential silica exposure was based on the decedent's usual industry and occupation. Assignment of potential exposure to silica was based on the entire range of industries and occupations. Odds ratios (ORs) for mortality from respiratory TB associated with potential high and intermediate exposures to silica were 1.30 (95% CI 1.14-1.48) and 1.07 (95% CI 0.77-1.47), respectively, adjusting for silicosis, other pneumoconioses, age, gender, race, socioeconomic status, and potential exposure to active TB. The elevated OR was seen in all subgroups: male, female, white, and black. The average age at death among respiratory TB cases with potential silica exposure was significantly younger by four years than that among cases without potential silica exposure. The findings suggest that potential occupational exposure to silica alone, in the absence of silicosis, is associated with respiratory TB mortality, with a dose-response relationship.
Carol A. Burnett, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226, USA