Exposure-response relationships for silicosis and its progression in industrial sand workers

Objectives: This study aimed to characterize the relationship between radiographic silicosis and exposure to respirable quartz and determine how exposure affects disease progression.
Methods: Surveillance chest radiographs from a cohort of 1902 workers were examined to identify 67 cases of radiographic silicosis and 167 matched controls. Exposures were estimated by linking work histories to a job exposure matrix (JEM) based on samples collected by the participating companies and historical estimates. Conditional logistic regression was used to examine exposure-response relationships. Sequential radiographs from silicosis cases were used to assess associations between exposure and disease progression.
Results: Risk of silicosis increased with cumulative exposure [odds ratio (OR) 1.43 per 1 mg/m3 years, 95% confidence interval (CI) 1.23–1.66], average exposure concentration (OR 1.30 per 0.10 mg/m3, 95% CI 1.11–1.51) and net exposure duration (OR 1.10 per year, 95% CI 1.05–1.16). Multivariate analyses indicated that the risk associated with cumulative exposure varied depending on exposure duration and concentration. Analysis of the time worked at differing exposure levels indicated that exposures ≤0.05 mg/m3 were not significantly associated with silicosis risk after adjustment for years worked at higher concentrations. Disease progression was related to subsequent exposure concentration, with a yearly increase in small opacity profusion of 0.052 subcategory per each 0.10 mg/m3 increase in concentration.
Conclusions: Workers with longer exposure at lower concentrations were at higher risk for silicosis than those with the same cumulative exposure who worked for a shorter time at higher concentrations. The rate of silicosis progression was related to subsequent exposure concentration.

Source: Vacek, P.M., Glenn, R.E., Rando, R.J., Parker, J.E., Kanne, J.P., Henry, D.A., Meyer, C.A. (2018). Scandinavian Journal of Work, Environment & Health.

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