Skip Navigation LinksHome > September 2013 - Volume 55 - Issue 9 > Threshold Value Estimation for Respirable Quartz Dust Exposu...
Journal of Occupational & Environmental Medicine:
doi: 10.1097/JOM.0b013e318297327a
Original Articles

Threshold Value Estimation for Respirable Quartz Dust Exposure and Silicosis Incidence Among Workers in the German Porcelain Industry

Morfeld, Peter PD; Mundt, Kenneth A. Dr med; Taeger, Dirk Dr med; Guldner, Karlheinz Dr med; Steinig, Othmar Dipl-Ing; Miller, Brian G. Dr med

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Objectives: To estimate a threshold value for the respirable quartz dust concentration and silicosis incidence (1/1, ILO 1980/2000) in the German porcelain worker cohort.

Methods: Forty incident cases occurred among 17,144 workers. Estimation of the relationship to cumulative respirable quartz dust exposures by using Cox regression with restricted cubic splines (7 knots or less) and fractional polynomials (degrees 5 or less). Threshold estimates were obtained by subtracting candidate values from the time-dependent concentration data (setting the result to zero if negative) and recalculating cumulative exposure.

Results: Best threshold estimate was 0.25 mg/m3 (95% confidence interval: 0.15 to 0.30 mg/m3).

Conclusions: A concentration threshold for silicosis risk is plausible. A threshold Cox model fitted the data significantly better than a nonthreshold model, summarized the cohort information without a loss in extracted information and more simply than restricted cubic splines and fractional polynomials.

Copyright © 2013 by the American College of Occupational and Environmental Medicine


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