Gibb et al. Respond

Abstract

We thank Zhou for his interest in our study; however, his letter misquotes our article. He states that we reported that our proportionate mortality ratio (PMR) for mesothelioma was “the highest PMR ever observed and more than an order of magnitude higher than any other published studies.” We stated that the PMR for mesothelioma was the highest of those in our study. We did not state that it was the highest PMR ever observed. We also did not state that the PMR was an order of magnitude higher than “any other published studies.” We stated that the PMR was an order of magnitude higher than that for any occupation reported by McElvenny et al.1 Zhou claims that the National Institute for Occupational Safety and Health Life Table Analysis System (LTAS; National Institute for Occupational Safety and Health, Atlanta, GA) overestimated the PMR for mesothelioma because 6 of 7 mesothelioma deaths occurred prior to 1999, the year when the International Classification of Diseases, 10th Revision (ICD-10) was implemented. All deaths in our study were coded to ICD10. The LTAS manual does not indicate the program cannot be used if mesothelioma deaths occurred prior to 1999 nor did the program produce error messages when we ran the analysis. Since our analysis, 11 more deaths have been added to the US Transuranium and Uranium Registries. Mesothelioma was reported to be the underlying cause of one of these deaths and to contribute to another death for which the immediate cause was reported as “pneumonic.” Zhou’s presumed approach would be to calculate a PMR only for the two post-1998 deaths for which mesothelioma was the underlying cause. Given that only 73 of the deaths in the Registries occurred after 1998, this approach could well produce a PMR for mesothelioma that has confidence limits inclusive of the PMR that we found. Regardless of whether LTAS is used to produce a PMR for mesothelioma using all deaths in the Registries or only deaths occurring after 1998, there is no question that the proportion attributed to mesothelioma is significantly elevated. In addition to those deaths for which mesothelioma was reported to be the underlying cause, one individual was found to have mesothelioma at autopsy (the original cause was reported to be lung cancer), and mesothelioma was reported to be a contributory cause in another death (described above). This means that there are now 10 individuals who had mesothelioma among the 340 workers in the Registries who were occupationally exposed to radiation. By any measure, that is a significant number, and it would be disingenuous to ignore it.