Analysis of occupational asbestos exposure and lung cancer mortality using the g formula

Abstract

We employed the parametric G formula to analyze lung cancer mortality in a cohort of textile manufacturing workers who were occupationally exposed to asbestos in South Carolina. A total of 3,002 adults with a median age of 24 years at enrollment (58% male, 81% Caucasian) were followed for 117,471 person-years between 1940 and 2001, and 195 lung cancer deaths were observed. Chrysotile asbestos exposure was measured in fiber-years per milliliter of air, and annual occupational exposures were estimated on the basis of detailed work histories. Sixteen percent of person-years involved exposure to asbestos, with a median exposure of 3.30 fiber-years/mL among those exposed. Lung cancer mortality by age 90 years under the observed asbestos exposure was 9.44%. In comparison with observed asbestos exposure, if the facility had operated under the current Occupational Safety and Health Administration asbestos exposure standard of <0.1 fibers/mL, we estimate that the cohort would have experienced 24% less lung cancer mortality by age 90 years (mortality ratio = 0.76, 95% confidence interval: 0.62, 0.94). A further reduction in asbestos exposure to a standard of <0.05 fibers/mL was estimated to have resulted in a minimal additional reduction in lung cancer mortality by age 90 years (mortality ratio = 0.75, 95% confidence interval: 0.61, 0.92).

Keywords: asbestos; bias (epidemiology); epidemiologic methods; healthy worker effect; occupations.

Figure 1.

Number of persons at risk for lung cancer mortality (solid curve) and number of cases of lung cancer death (solid vertical lines) by age among 3,002 South Carolina textile workers exposed to asbestos, during 117,471 person-years of follow-up between 1940 and 2001.

Figure 2.

Cumulative lung cancer mortality according to asbestos exposure in the observed data (gray line) and under the simulated natural course of exposure (black line) among 3,002 South Carolina textile workers during 117,471 person-years of follow-up between 1940 and 2001.

Figure 3.

Cumulative lung cancer mortality according to asbestos exposure under the simulated natural course of exposure (solid black line) and under simulated exposure to asbestos at a level of <5 fiber-years/mL (long-dashed black line), <2 fiber-years/mL (short-dashed black line), <0.1 fiber-years/mL (short- and long-dashed black line), and <0.05 fiber-years/mL (solid gray line) among 3,002 South Carolina textile workers during 117,471 person-years of follow-up between 1940 and 2001.