Adjusting for the reduced sensitivity of CXR in the dose-response relationship between cumulative silica exposure and silicosis in miners

IntroductionA recent meta-analysis confirmed that Chest Xray (CXR) has low sensitivity for the diagnosis of silicosis however the impact of this is unclear. We therefore re- estimated a previously published dose-response relationship between cumulative respirable crystalline silica (RCS) exposure and silicosis risk, under the assumptions that sensitivity was either fixed or relative to the population proportion of severe silicosis. MethodsWe combined unpublished logistic regression models from Scottish coal miners with meta-analysis results to model how CXR sensitivity changed according to cumulative RCS exposure. Among mining cohorts, we calculated the difference in the cumulative risk of silicosis between the unadjusted, and fixed and relative scenarios. Finally, we re-estimated the dose-response meta-analysis and related absolute risk reductions (ARR). ResultsIn all mining cohorts the cumulative risk of silicosis was substantially higher in both the fixed and relative sensitivity scenarios compared to the unadjusted estimate. This was most pronounced in the relative scenario and when cumulative RCS exposures were below approximately 6 mg/m3-years. A reduction from 4 to 2 mg/m3-years in cumulative RCS exposure corresponded to larger ARRs in the fixed and relative scenario than the unadjusted scenario; 409 (374, 434) and 557 (451, 620) cases per 1000 miners compared to 323 (298, 344) cases per 1000 miners, respectively. DiscussionWe were reliant on a single estimate of the proportion of severe disease to link sensitivity and cumulative RCS exposure. Nevertheless, adjusting for the low sensitivity of CXR for silicosis results in meaningful increased risks of silicosis in previously published mining cohorts.