Obtaining vital status and cause of death on a million persons.

PURPOSE: To present the methodology used to determine vital status and obtain cause of death (COD) within the Million Person Study of Low-Dose Health Effects (MPS). Data sources and vital status tracing techniques used to obtain vital status and COD for six (n = 424,238 subjects) of the ∼20+ cohorts under study are described. METHODS AND MATERIALS: A multistage approach using multiple sources of vital status information was used to determine vital status (or 'trace') study participants from as early as 1940 to the present. Mortality records from state departments of vital statistics and the Social Security Administration Death Master File (SSA-DMF) were matched to study participants by Social Security Number (SSN), full name, date of birth (DOB), and/or sex using deterministic and probabilistic algorithms. The National Death Index (NDI) and SSA Service for Epidemiological Researchers (SSA-SER) were used to obtain COD (after 1978) and verification of alive status, respectively. Online public records and ancestry services, death certificates, and specialized mortality sources were also utilized. RESULTS: For the MPS cohorts traced to date (nuclear power plant workers, industrial radiographers, atomic veterans, and workers at Rocketdyne/Atomics International, Mound nuclear facility, and Mallinckrodt Chemical Works), vital status was confirmed for over 90% of all study subjects in all but one cohort (88%). The ascertainment of COD was over 96% for all cohorts. CONCLUSIONS: A hallmark of a high-quality epidemiologic cohort mortality study is a low percentage of subjects with unknown vital status and a low percentage of deaths without a COD. The sources and methods used for vital status tracing and COD determination for the MPS have been successful and should be useful for other investigators tracing large, historic study populations. Some of the approaches would be applicable for use in all cohort studies using regional-specific mortality data or modifications to the approach.

Mesothelioma mortality within two radiation monitored occupational cohorts.

PURPOSE: The risk of mesothelioma, including cancers of the pleura and peritoneum, was examined within two large cohorts of workers monitored for exposure to ionizing radiation. METHODS AND MATERIALS: Mortality was assessed among 253,632 workers routinely monitored for external radiation, including 30,724 industrial radiographers (IR) at shipyards, 142,583 workers at nuclear power plants (NPP), and 83,441 IR who had not worked at an NPP or shipyard. Follow-up was from 1969 through 2011. Standardized mortality ratios (SMRs) and 95% confidence intervals (CIs) were computed; observed numbers of deaths from mesothelioma (including cancers of the pleura and peritoneum) and asbestosis were compared with numbers expected based on age-, sex-, and calendar year-specific national mortality rates. Job history and quantitative asbestos exposure data were unavailable, but work at a shipyard was taken as a surrogate for the likelihood of exposure. Cox proportional hazards models were used to estimate hazard ratios (HRs) for mesothelioma in relation to estimated cumulative radiation exposure to the lung. RESULTS: The mean duration of follow-up was 25.3 years (max 42 years). The mean cumulative lung dose was 28.6 mGy (7.3% > 250 mGy). Nearly 20% of the workers had died by 2011. A total of 421 mesothelioma deaths were found (75% occurring after 1999) with increased SMRs among workers monitored in shipyards (SMR 9.97; 95% CI 8.50-11.63) and for NPP workers (SMR 5.55; 95% CI 4.88-6.29), but not for IR who had not worked in shipyards (SMR 1.15; 95% CI 0.53-2.19). Likewise, deaths from asbestosis (n = 189) were also increased for shipyard and NPP workers (SMR = 18.1 and 9.2, respectively), but not among workers who never worked at a shipyard or NPP (SMR = 0.70; n = 1). Radiation dose to the lung was not associated with a statistically meaningful dose-response trend for mesothelioma in the combined cohorts (HR at 100 mGy = 1.10; 95% CI 0.96-1.27; p = .18), nor was mesothelioma risk associated with radiation exposure among IR who had not worked in a shipyard and assumed minimally exposed to asbestos. CONCLUSIONS: An elevated rate of death from mesothelioma was observed in two radiation-exposed occupational groups with potential for asbestos exposure. The increased risk of death from asbestosis, combined with little evidence of a rising trend in mesothelioma mortality with increasing radiation exposure, suggests that the mesothelioma (and asbestosis) excess in these workers was due to asbestos exposure in shipyards and power plants and not to occupational low-dose radiation.