Lifetime excess absolute risk for lung cancer due to exposure to radon: results of the pooled uranium miners cohort study PUMA.

The Pooled Uranium Miners Analysis (PUMA) study is the largest uranium miners cohort with 119,709 miners, 4.3 million person-years at risk and 7754 lung cancer deaths. Excess relative rate (ERR) estimates for lung cancer mortality per unit of cumulative exposure to radon progeny in working level months (WLM) based on the PUMA study have been reported. The ERR/WLM was modified by attained age, time since exposure or age at exposure, and exposure rate. This pattern was found for the full PUMA cohort and the 1960 + sub-cohort, i.e., miners hired in 1960 or later with chronic low radon exposures and exposure rates. The aim of the present paper is to calculate the lifetime excess absolute risk (LEAR) of lung cancer mortality per WLM using the PUMA risk models, as well as risk models derived in previously published smaller uranium miner studies, some of which are included in PUMA. The same methods were applied for all risk models, i.e., relative risk projection up to <95 years of age, an exposure scenario of 2 WLM per year from age 18-64 years, and baseline mortality rates representing a mixed Euro-American-Asian population. Depending upon the choice of model, the estimated LEAR per WLM are 5.38 × 10-4 or 5.57 × 10-4 in the full PUMA cohort and 7.50 × 10-4 or 7.66 × 10-4 in the PUMA 1960 + sub-cohort, respectively. The LEAR per WLM estimates derived from risk models reported for previously published uranium miners studies range from 2.5 × 10-4 to 9.2 × 10-4. PUMA strengthens knowledge on the radon-related lung cancer LEAR, a useful way to translate models for policy purposes.

Mortality among uranium miners in North America and Europe: the Pooled Uranium Miners Analysis (PUMA).

BACKGROUND: The Pooled Uranium Miners Analysis (PUMA) study draws together information from cohorts of uranium miners from Canada, the Czech Republic, France, Germany and the USA. METHODS: Vital status and cause of death were ascertained and compared with expectations based upon national mortality rates by computing standardized mortality ratios (SMRs) overall and by categories of time since first hire, calendar period of first employment and duration of employment as a miner. RESULTS: There were 51 787 deaths observed among 118 329 male miners [SMR = 1.05; 95% confidence interval (CI): 1.04, 1.06]. The SMR was elevated for all cancers (n = 16 633, SMR = 1.23; 95% CI: 1.21, 1.25), due primarily to excess mortality from cancers of the lung (n = 7756, SMR = 1.90; 95% CI: 1.86, 1.94), liver and gallbladder (n = 549, SMR = 1.15; 95% CI: 1.06, 1.25), larynx (n = 229, SMR = 1.10; 95% CI: 0.97, 1.26), stomach (n = 1058, SMR = 1.08; 95% CI: 1.02, 1.15) and pleura (n = 39, SMR = 1.06; 95% CI: 0.75, 1.44). Lung-cancer SMRs increased with duration of employment, decreased with calendar period and persisted with time since first hire. Among non-malignant causes, the SMR was elevated for external causes (n = 3362, SMR = 1.41; 95% CI: 1.36, 1.46) and respiratory diseases (n = 4508, SMR = 1.32; 95% CI: 1.28, 1.36), most notably silicosis (n = 814, SMR = 13.56; 95% CI: 12.64, 14.52), but not chronic obstructive pulmonary disease (n = 1729, SMR = 0.98; 95% CI: 0.93, 1.02). CONCLUSIONS: Whereas there are important obstacles to the ability to detect adverse effects of occupational exposures via SMR analyses, PUMA provides evidence of excess mortality among uranium miners due to a range of categories of cause of death. The persistent elevation of SMRs with time since first hire as a uranium miner underscores the importance of long-term follow-up of these workers.

Dose Estimation for a Study of Nuclear Workers in France, the United Kingdom and the United States of America: Methods for the International Nuclear Workers Study (INWORKS).

In the framework of the International Nuclear Workers Study conducted in France, the UK and the U.S. (INWORKS), updated and expanded methods were developed to convert recorded doses of ionizing radiation to estimates of organ doses or individual personal dose equivalent [H(p)(10)] for a total number of 308,297 workers, including 40,035 women. This approach accounts for differences in dosimeter response to predominant workplace energy and geometry of exposure and for the recently published ICRP report on dose coefficients for men and women separately. The overall mean annual individual personal dose equivalent, including zero doses, is 1.73 mSv [median = 0.42; interquartile range (IQR): 0.07, 1.59]. Associated individual organ doses were estimated. INWORKS includes workers who had potential for exposure to neutrons. Therefore, we analyzed neutron dosimetry data to identify workers potentially exposed to neutrons. We created a time-varying indicator for each worker, classifying them according to whether they had a positive recorded neutron dose and if so, whether their neutron dose ever exceeded 10% of their total external penetrating radiation dose. The number of workers flagged as being exposed to neutrons was 13% for the full cohort, with 15% of the cohort in France, 12% of the cohort in the UK and 14% in the U.S. We also used available information on in vivo and bioassay monitoring to identify workers with known depositions or suspected internal contaminations. As a result of this work, information is now available that will allow various types of sensitivity analyses.

The effects of building-related factors on classroom relative humidity among North Carolina schools participating in the 'Free to Breathe, Free to Teach' study.

UNLABELLED: Both high and low indoor relative humidity (RH) directly impact Indoor Air Quality (IAQ), an important school health concern. Prior school studies reported a high prevalence of mold, roaches, and water damage; however, few examined associations between modifiable classroom factors and RH, a quantitative indicator of dampness. We recorded RH longitudinally in 134 North Carolina classrooms (n = 9066 classroom-days) to quantify the relationships between modifiable classroom factors and average daily RH below, within, or above levels recommended to improve school IAQ (30-50% or 30-60% RH). The odds of having high RH (>60%) were 5.8 [95% Confidence Interval (CI): 2.9, 11.3] times higher in classrooms with annual compared to quarterly heating, ventilating, and air-conditioning (HVAC) system maintenance and 2.5 (95% CI: 1.5, 4.2) times higher in classrooms with HVAC economizers compared to those without economizers. Classrooms with direct-expansion split systems compared to chilled water systems had 2.7 (95% CI: 1.7, 4.4) times higher odds of low RH (<30%). When unoccupied, classrooms with thermostat setbacks had 3.7 (95% CI: 1.7, 8.3) times the odds of high RH (>60%) of those without setbacks. This research suggests actionable decision points for school design and maintenance to prevent high or low classroom RH. PRACTICAL IMPLICATIONS: This study combines longitudinal measurements of classroom relative humidity with school inspection data from several schools to describe the problem of relative humidity control in schools. Our findings on how maintenance and mechanical factors affect classroom humidity provide suggestions on building operations policies and heating, ventilating, and air-conditioning (HVAC) design considerations that may improve classroom relative humidity control.

Mortality associated with chronic external radiation exposure in the French combined cohort of nuclear workers.

OBJECTIVE: The long-term effects of protracted low level ionising radiation exposure are investigated in a combined analysis of French nuclear workers employed by the Commissariat à l'Energie Atomique (CEA), AREVA Nuclear Cycle (AREVA NC) and Electricité de France (EDF). Associations between cumulative external radiation dose and mortality due to solid cancers, leukaemia and circulatory disease were examined. METHODS: All workers hired by CEA, AREVA NC and EDF between 1950 and 1994 who were employed for at least 1 year, badge-monitored for radiation exposure and alive on 1 January 1968 were included. Individual data of annual exposure to penetrating photons (X-rays and gamma rays) were reconstructed for each worker. Estimates of radiation dose-mortality associations were obtained using a linear excess relative risk (ERR) Poisson regression model. RESULTS: Among the 59 021 nuclear workers, 2312 died of solid cancer, 78 of leukaemia and 1468 of circulatory diseases during the 1968-2004 period. Approximately 72% of the cohort had a non-zero cumulative radiation dose estimate, with a mean cumulative dose of 22.5 mSv. Positive but non-significant ERR/Sv were observed for all solid cancers, leukaemia excluding chronic lymphocytic leukaemia (CLL), ischaemic heart diseases and cerebrovascular diseases. A significant ERR/Sv was found for myeloid leukaemia. CONCLUSIONS: This is the first combined analysis of major French cohorts of nuclear workers. Results were consistent with risks estimated in other nuclear worker cohorts and illustrate the potential of a further joint international study to yield direct risk estimates in support to radiation protection standards.

Physical assault among nursing staff employed in acute care.

Hospital workers are known to be at risk of physical assault. The objective of this study is to characterize injuries resulting from physical assault among hospital nursing staff and to identify associated risk factors. Workers' compensation reports linked to human resources data were used to identify a cohort of aides and nurses employed in acute care units at a major healthcare system from 1997 to 2004 and their reported physical assault events. Poisson regression methods were used to estimate rates and rate ratios (RR) by occupation, gender, race, age, tenure, and hospital unit. During the study period 220 assaults were reported; the overall incidence rate was 1.65 (95% CI: 1.45-1.89) per 100 full-time-equivalent employees (FTEs). Assault risk was higher among those with shorter tenure (< 5 years vs. 15 or more) (RR=1.35, 95% CI: 0.83-2.19) and younger workers (under age 30 vs. 50 or older) (RR=1.30, 95% CI: 0.78-2.19), and lower among Black workers (vs. non-Blacks) (RR=0.63, 95% CI: 0.45-0.90). Incidence rates were highest in Psychiatry (12.65, 95% CI: 8.90-17.99), Neurology (4.43, 95% CI: 3.17-6.20) and Rehabilitation (3.63, 95% CI: 1.51-8.71) units. Interventions targeting Psychiatry, Neurology, and Rehabilitation units, and younger and newly hired staff are warranted. More detailed data are needed to develop targeted interventions.

Discrete time hazards models for occupational and environmental cohort analyses.

OBJECTIVE: To discuss the use of discrete time hazards models for the analysis of occupational and environmental cohort data. METHODS: Analytical data structures and regression methods for discrete time hazards models are described. This approach is illustrated via analyses of data from a study of mortality in a cohort of chemical workers exposed to dioxin. RESULTS AND CONCLUSIONS: Analyses employing a discrete time hazards model facilitate examination of observed and expected counts, the calculation of attributable fractions, and empirical description of the estimated hazard rates. In addition, this approach can be used to fit non-multiplicative models, such as the linear hazards ratio model (which has been employed in epidemiological analyses of a variety of environmental and occupational exposures).

Occupational injuries among aides and nurses in acute care.

BACKGROUND: Occupational injuries are common among nursing personnel. Most epidemiologic research on nursing aides comes from long-term care settings. Reports from acute care settings often combine data on nurses and aides even though their job requirements and personal characteristics are quite different. Our objective was to assess risk of work-related injuries in an acute care setting while contrasting injuries of aides and nurses. METHODS: A retrospective cohort of aides (n = 1,689) and nurses (n = 5,082) working in acute care at a large healthcare system between 1997 and 2004 were identified via personnel records. Workers' compensation filings were used to ascertain occupational injuries. Poisson regression was used to estimate rate ratios (RR) and 95% confidence intervals (95% CI). RESULTS: Aides had higher overall injury rates than nurses for no-lost work time (RR = 1.2, 95% CI: 1.1-1.3) and lost work time (RR = 2.8, 95% CI: 2.1-3.8) injuries. The risk of an injury due to lifting was greater among aides compared to nurses for both non-lost work time and lost work time injuries. Injury rates among aides were particularly high in rehabilitation and orthopedics units. Most of the injuries requiring time away from work for both groups were related to the process of delivering direct patient care. CONCLUSIONS: Our findings illustrate the importance of evaluating work-related injuries separately for aides and nurses, given differences in injury risk profiles and injury outcomes. It is particularly important that occupational safety needs of aides be addressed as this occupation experiences significant job growth.

Lung cancer mortality and fibre exposures among North Carolina asbestos textile workers.

OBJECTIVE: To describe mortality among workers exposed to chrysotile asbestos and evaluate the relationship between lung cancer and asbestos fibre exposure. METHODS: Workers employed for at least 1 day between 1 January 1950 and 31 December 1973 in any of four plants in North Carolina, USA that produced asbestos textile products were enumerated. Vital status was ascertained through 31 December 2003. Historical exposures to asbestos fibres were estimated from work histories and 3578 industrial hygiene measurements taken in 1935-1986. Mortality of the cohort was compared with that of the national population via standardised mortality ratios (SMRs). Exposure-response relationships for lung cancer were examined within the cohort using Poisson regression to compute adjusted mortality rate ratios. RESULTS: Follow-up of 5770 workers included in the cohort resulted in 181 640 person-years of observation, with 2583 deaths from all causes and 277 from lung cancer. Mortality from all causes, all cancers and lung cancer was significant higher than expected, with SMRs of 1.47 for all causes, 1.41 for all cancer and 1.96 (95% CI 1.73 to 2.20) for lung cancer. SMRs for pleural cancer, mesothelioma and pneumoconiosis were also elevated. The risk of lung cancer and asbestosis increased with cumulative fibre exposure (RR 1.102 per 100 fibre-year/ml, 95% CI 1.044 to 1.164, and RR 1.249 per 100 fibre-year/ml, 95% CI 1.186 to 1.316, respectively, for total career exposure). CONCLUSIONS: This study provides further evidence that exposure to chrysotile asbestos in textile manufacturing is associated with increased risk of lung cancer, asbestosis cancer of the pleura and mesothelioma.

The 15-Country Collaborative Study of Cancer Risk among Radiation Workers in the Nuclear Industry: estimates of radiation-related cancer risks.

A 15-Country collaborative cohort study was conducted to provide direct estimates of cancer risk following protracted low doses of ionizing radiation. Analyses included 407,391 nuclear industry workers monitored individually for external radiation and 5.2 million person-years of follow-up. A significant association was seen between radiation dose and all-cause mortality [excess relative risk (ERR) 0.42 per Sv, 90% CI 0.07, 0.79; 18,993 deaths]. This was mainly attributable to a dose-related increase in all cancer mortality (ERR/Sv 0.97, 90% CI 0.28, 1.77; 5233 deaths). Among 31 specific types of malignancies studied, a significant association was found for lung cancer (ERR/Sv 1.86, 90% CI 0.49, 3.63; 1457 deaths) and a borderline significant (P = 0.06) association for multiple myeloma (ERR/Sv 6.15, 90% CI <0, 20.6; 83 deaths) and ill-defined and secondary cancers (ERR/Sv 1.96, 90% CI -0.26, 5.90; 328 deaths). Stratification on duration of employment had a large effect on the ERR/Sv, reflecting a strong healthy worker survivor effect in these cohorts. This is the largest analytical epidemiological study of the effects of low-dose protracted exposures to ionizing radiation to date. Further studies will be important to better assess the role of tobacco and other occupational exposures in our risk estimates.

The impact on relative risk estimates of inconsistencies between ICD-9 and ICD-10.

BACKGROUND: The 10th revision of the International Classification of Diseases (ICD) represents a major change in the ICD system. This paper investigates the impact on relative risk estimates of inconsistencies in outcome classification between ICD-9 and ICD-10, including scenarios in which occupational exposure levels are correlated with year of death (and therefore with the ICD revision in effect at death). The setting of interest is a cohort mortality study in which follow up spans the periods during which ICD-9 and ICD-10 were in effect. The relative risk estimate obtained when death certificates are coded to the ICD revision in effect at time of death is compared to the relative risk estimate that would be obtained if all death certificates were coded to a consistent ICD revision (that is, ICD-10). The ratio of these relative risks is referred to as the coefficient of bias. METHODS: Simple equations relate the coefficient of bias to the sensitivity and specificity of the classification of decedents into categories of cause of death via ICD-9 (treating classifications based upon ICD-10 as the standard). Bridge coded mortality data for 2,296,922 decedents (that is, death certificates coded to ICD-9 and ICD-10) are used to derive estimates of sensitivity and specificity by category of cause of death. Numerical examples illustrate the application of these equations. RESULTS: Estimates of the sensitivity of classification of decedents into categories of death defined by ICD-9 ranged from 0.26-1.00. Specificity was above 0.98 for all categories of cause of death. Numerical examples illustrate that inconsistencies in outcome classification between ICD-9 and ICD-10 may have substantial impact on relative risk estimates if there is a strong relation between exposure status and the proportion of deaths coded to a given ICD revision. CONCLUSIONS: For analyses of mortality outcomes that exhibit poor comparability between ICD-9 and -10, it may be prudent to recode cause of death information to a standard ICD revision in order to avoid bias that can occur when exposures are correlated with the proportion of deaths coded to a given ICD revision.

Investigating time patterns of variation in radiation cancer associations.

AIMS: In occupational settings, carcinogenic exposures are often repeated or protracted over time. The time pattern of exposure accrual may influence subsequent temporal patterns of cancer risk. The authors present several simple models that may be used to evaluate the influence of time since exposure or age at exposure on cancer incidence or mortality in an occupational cohort. METHODS: A cohort of 40,415 nuclear industry workers was identified via the Canadian National Dose Registry. Vital status and cause of death were ascertained through 1994. Associations between ionising radiation and mortality due to lung cancer, leukaemia, and cancers other than lung and leukaemia were quantified using conditional logistic regression models with risk sets constructed by incidence density sampling. A step function, a bilinear function, and a sigmoid function were used to evaluate temporal variation in exposure effects. RESULTS: Step and sigmoid functions were used to explore latency and morbidity periods. For analyses of lung cancer, leukaemia, and other cancers the best fitting models were obtained when exposure assignment was lagged by 13, 0, and 5 years, respectively. A bilinear function was used to evaluate whether exposure effects diminished with time since exposure. In analyses of lung cancer and leukaemia, there was evidence that radiation effects attenuated with protracted time since exposure. In analyses of age at exposure, there was evidence of variation in radiation mortality associations for analyses of lung cancer and leukaemia; discounting radiation doses accrued at younger ages (for example, 15-35 years) led to significant improvements in model fit. CONCLUSIONS: This paper illustrates empirical approaches to evaluating temporal variation in the effect of a protracted exposure on disease risk.

Risk of cancer after low doses of ionising radiation: retrospective cohort study in 15 countries.

OBJECTIVES: To provide direct estimates of risk of cancer after protracted low doses of ionising radiation and to strengthen the scientific basis of radiation protection standards for environmental, occupational, and medical diagnostic exposures. DESIGN: Multinational retrospective cohort study of cancer mortality. SETTING: Cohorts of workers in the nuclear industry in 15 countries. PARTICIPANTS: 407 391 workers individually monitored for external radiation with a total follow-up of 5.2 million person years. MAIN OUTCOME MEASUREMENTS: Estimates of excess relative risks per sievert (Sv) of radiation dose for mortality from cancers other than leukaemia and from leukaemia excluding chronic lymphocytic leukaemia, the main causes of death considered by radiation protection authorities. RESULTS: The excess relative risk for cancers other than leukaemia was 0.97 per Sv, 95% confidence interval 0.14 to 1.97. Analyses of causes of death related or unrelated to smoking indicate that, although confounding by smoking may be present, it is unlikely to explain all of this increased risk. The excess relative risk for leukaemia excluding chronic lymphocytic leukaemia was 1.93 per Sv (< 0 to 8.47). On the basis of these estimates, 1-2% of deaths from cancer among workers in this cohort may be attributable to radiation. CONCLUSIONS: These estimates, from the largest study of nuclear workers ever conducted, are higher than, but statistically compatible with, the risk estimates used for current radiation protection standards. The results suggest that there is a small excess risk of cancer, even at the low doses and dose rates typically received by nuclear workers in this study.

Age at exposure to ionising radiation and cancer mortality among Hanford workers: follow up through 1994.

BACKGROUND: Studies of workers at the plutonium production factory in Hanford, WA have led to conflicting conclusions about the role of age at exposure as a modifier of associations between ionising radiation and cancer. AIMS: To evaluate the influence of age at exposure on radiation risk estimates in an updated follow up of Hanford workers. METHODS: A cohort of 26 389 workers hired between 1944 and 1978 was followed through 1994 to ascertain vital status and causes of death. External radiation dose estimates were derived from personal dosimeters. Poisson regression was used to estimate associations between mortality and cumulative external radiation dose at all ages, and in specific age ranges. RESULTS: A total of 8153 deaths were identified, 2265 of which included cancer as an underlying or contributory cause. Estimates of the excess relative risk per Sievert (ERR/Sv) for cumulative radiation doses at all ages combined were negative for all cause and leukaemia and positive for all cancer and lung cancer. Cumulative doses accrued at ages below 35, 35-44, and 45-54 showed little association with mortality. For cumulative dose accrued at ages 55 and above (10 year lag), the estimated ERR/Sv for all cancers was 3.24 (90% CI: 0.80 to 6.17), primarily due to an association with lung cancer (ERR/Sv: 9.05, 90% CI: 2.96 to 17.92). CONCLUSIONS: Associations between radiation and cancer mortality in this cohort are primarily a function of doses at older ages and deaths from lung cancer. The association of older age radiation exposures and cancer mortality is similar to observations from several other occupational studies.

Poisson regression analysis of ungrouped data.

BACKGROUND: Poisson regression is routinely used for analysis of epidemiological data from studies of large occupational cohorts. It is typically implemented as a grouped method of data analysis in which all exposure and covariate information is categorised and person-time and events are tabulated. AIMS: To describe an alternative approach to Poisson regression analysis using single units of person-time without grouping. METHODS: Data for simulated and empirical cohorts were analysed by Poisson regression. In analyses of simulated data, effect estimates derived via Poisson regression without grouping were compared to those obtained under proportional hazards regression. Analyses of empirical data for a cohort of 138 900 electrical workers were used to illustrate how the ungrouped approach may be applied in analyses of actual occupational cohorts. RESULTS: Using simulated data, Poisson regression analyses of ungrouped person-time data yield results equivalent to those obtained via proportional hazards regression: the results of both methods gave unbiased estimates of the "true" association specified for the simulation. Analyses of empirical data confirm that grouped and ungrouped analyses provide identical results when the same models are specified. However, bias may arise when exposure-response trends are estimated via Poisson regression analyses in which exposure scores, such as category means or midpoints, are assigned to grouped data. CONCLUSIONS: Poisson regression analysis of ungrouped person-time data is a useful tool that can avoid bias associated with categorising exposure data and assigning exposure scores, and facilitate direct assessment of the consequences of exposure categorisation and score assignment on regression results.

An incidence density sampling program for nested case-control analyses.

BACKGROUND: The nested case-control design can be a very efficient approach to an epidemiological investigation. In order to obtain unbiased estimates of relative risk, controls should be selected by incidence density sampling, which involves matching each case to a sample of those who are at risk at the time of case occurrence. METHODS: This paper presents a simple computer program for incidence density sampling. This program was evaluated using data derived from a cohort study of mortality among workers employed in the nuclear weapons industry. Controls were selected for cases via incidence density sampling; an estimate of the exposure-mortality association was obtained via conditional logistic regression. After 100 iterations of this procedure, the average effect estimate was compared to the risk estimate obtained via proportional hazards regression. The same methods were used to evaluate a program for incidence density sampling that was proposed previously by Pearce in 1989. RESULTS: Relative risk estimates obtained from nested case-control analyses conducted using the incidence density sampling program reported in this paper are unbiased. In contrast, the program for incidence density sampling proposed by Pearce tended to produce biased relative risk estimates; the magnitude of bias increased with increasing numbers of controls selected per case. CONCLUSIONS: The computer program described in this paper offers a simple approach to incidence density sampling for nested case-control analyses with exact matching on attained age and appropriate enumeration of the pool of eligible controls for each case. This method overcomes problems of bias inherent in a previously proposed program for incidence density sampling.

The impact of exposure categorisation for grouped analyses of cohort data.

BACKGROUND: Poisson regression is routinely used in occupational and environmental epidemiology. For typical Poisson regression analyses, person-time and events are tabulated by categorising predictor variables that were originally measured on a continuous scale. In order to estimate a dose-response trend, a researcher must decide how to categorise exposures and how to assign scores to exposure groups. AIMS: To investigate the impact on regression results of decisions about exposure categorisation and score assignment. METHODS: Cohort data were generated by Monte Carlo simulation methods. Exposure categories were defined by quintiles or deciles of the exposure distribution. Scores were assigned to exposure groups based on category midpoint and mean exposure levels. Estimated exposure-disease trends derived via Poisson regression were compared to the "true" association specified for the simulation. RESULTS: Under the assumption that exposures conform to a lognormal or exponential distribution, trend estimates tend to be negatively biased when scores are assigned based on category midpoints and positively biased when scores are assigned based on cell specific mean values. The degree of bias was greater when exposure categories were defined by quintiles of the exposure distribution than when categories were defined by deciles of the exposure distribution. CONCLUSIONS: The routine practice of exposure categorisation and score assignment introduces exposure misclassification that may be differential with respect to disease status and, consequently, lead to biased exposure-disease trend estimates. When using the Poisson regression method to evaluate exposure-disease trends, such problems can be minimised (but not necessarily eliminated) by forming relatively refined exposure categories based on percentiles of the exposure distribution among cases, and by assigning scores to exposure categories that reflect person-time weighted mean exposure levels.

Deindustrialisation and the long term decline in fatal occupational injuries.

AIMS: To examine the extent to which deindustrialisation accounts for long term trends in occupational injury risk in the United States. METHODS: Rates of fatal unintentional occupational injury were computed using data from death certificates and the population census. Trends were estimated using Poisson regression. Standardisation and regression methods were used to adjust for the potential effect of structural change in the labour market. RESULTS: The fatal occupational injury rate for all industries declined 45% from 1980 to 1996 (RR (rate ratio) 0.55, 95% CI 0.52 to 0.57). Adjustment for structural changes in the workforce shifted the RR to 0.62 (95% CI 0.60 to 0.65). Expanding industries enjoyed more rapid reduction in risk (-3.43% per year, 95% CI -3.62 to -3.24) than those that contracted (-2.65% per year, 95% CI -2.88 to -2.42). CONCLUSIONS: Deindustrialisation contributed to the decline of fatal occupational injury rates in the United States, but explained only 10-15% of the total change.

Cancer risk from low-level ionizing radiation: the role of age at exposure.

This article examines methodological issues related to epidemiologic investigations of the influence of age at exposure on radiation risk estimates; the epidemiologic literature on the role of age at exposure in radiation-cancer associations; and biological mechanisms that may account for associations observed in these studies. There is substantial evidence that young children, and especially the fetus, are highly vulnerable to ionizing radiation. Investigations also suggest that sensitivity may increase at the oldest ages of exposure. Further attention to modifying factors in radiation-cancer associations, such as age at exposure, may help to protect workers and the public by improving our understanding of sensitivity variation within populations.

Radiation and mortality of workers at Oak Ridge National Laboratory: positive associations for doses received at older ages.

We examined associations between low-level exposure to ionizing radiation and mortality among 14,095 workers hired at the Oak Ridge National Laboratory between 1943 and 1972. Workers at the facility were individually monitored for external exposure to ionizing radiation and have been followed through 1990 to ascertain cause of death information. Positive associations were observed between low-level exposure to external ionizing radiation and mortality. These associations were larger for doses received after 45 years of age, larger under longer lag assumptions, and primarily due to cancer causes of death. All cancer mortality was estimated to increase 4.98% [standard error (SE) = 1.5] per 10-mSv cumulative dose received after age 45 under a 10-year lag, and 7.31% (SE = 2.2) per 10-mSv cumulative dose received after age 45 under a 20-year lag. Associations between radiation dose and lung cancer were of similar magnitude to associations between radiation dose and all cancers except lung cancer. Nonmalignant respiratory disease exhibited a positive association with cumulative radiation dose received after age 45, whereas ischemic heart disease exhibited no association with radiation dose. These findings suggest increases in cancer mortality associated with low-level external exposure to ionizing radiation and potentially greater sensitivity to the carcinogenic effects of ionizing radiation with older ages at exposure.