A hybrid expert approach for retrospective assessment of occupational exposures in a population-based case-control study of cancer.

BACKGROUND: While the expert-based occupational exposure assessment approach has been considered the reference method for retrospective population-based studies, its implementation in large study samples has become prohibitive. To facilitate its application and improve upon it we developed, in the context of a Montreal population-based study of prostate cancer (PROtEuS), a hybrid approach combining job-exposure profiles (JEPs) summarizing expert evaluations from previous studies and expert review. We aim to describe the hybrid expert method and its impacts on the exposures assigned in PROtEuS compared to those from a previous study coded using the traditional expert method. METHODS: Applying the hybrid approach, experts evaluated semi-quantitative levels of confidence, concentration and frequency of exposure to 313 agents for 16,065 jobs held by 4005 subjects in PROtEuS. These assessments were compared to those from a different set of jobs coded in an earlier study of lung cancer, conducted on the same study base, for 90 blue-collar occupations and 203 agents. Endpoints evaluated included differences in the number of exposures and in the distribution of ratings across jobs, and the within-occupation variability in exposure. RESULTS: Compared to jobs from the lung cancer study, jobs in PROtEuS had on average 0.3 more exposures. PROtEuS exposures were more often assigned definite confidence ratings, but concentration and frequency levels tended to be lower. The within-occupation variability in ratings assigned to jobs were lower in PROtEuS jobs for all metrics. This was particularly evident for concentration, although considerable variability remained with over 40% of occupation/agent cells in PROtEuS exposed at different levels. The hybrid approach reduced coding time by half, compared to the traditional expert assessment. CONCLUSIONS: The new hybrid expert approach improved on efficiency and transparency, and resulted in greater confidence in assessments, compared to the traditional expert method applied in an earlier study involving a similar set of jobs. Assigned ratings were more homogeneous with the hybrid approach, possibly reflecting clearer guidelines for coding, greater coherence between experts and/or reliance on summaries of past assessments. Nevertheless, significant within-occupation variability remained with the hybrid approach, suggesting that experts took into account job-specific factors in their assessments.

Assessing occupational exposure to chemicals in an international epidemiological study of brain tumours.

The INTEROCC project is a multi-centre case-control study investigating the risk of developing brain cancer due to occupational chemical and electromagnetic field exposures. To estimate chemical exposures, the Finnish Job Exposure Matrix (FINJEM) was modified to improve its performance in the INTEROCC study and to address some of its limitations, resulting in the development of the INTEROCC JEM. An international team of occupational hygienists developed a crosswalk between the Finnish occupational codes used in FINJEM and the International Standard Classification of Occupations 1968 (ISCO68). For ISCO68 codes linked to multiple Finnish codes, weighted means of the exposure estimates were calculated. Similarly, multiple ISCO68 codes linked to a single Finnish code with evidence of heterogeneous exposure were refined. One of the key time periods in FINJEM (1960-1984) was split into two periods (1960-1974 and 1975-1984). Benzene exposure estimates in early periods were modified upwards. The internal consistency of hydrocarbon exposures and exposures to engine exhaust fumes was improved. Finally, exposure to polycyclic aromatic hydrocarbon and benzo(a)pyrene was modified to include the contribution from second-hand smoke. The crosswalk ensured that the FINJEM exposure estimates could be applied to the INTEROCC study subjects. The modifications generally resulted in an increased prevalence of exposure to chemical agents. This increased prevalence of exposure was not restricted to the lowest categories of cumulative exposure, but was seen across all levels for some agents. Although this work has produced a JEM with important improvements compared to FINJEM, further improvements are possible with the expansion of agents and additional external data.

A population-based case-control study of occupational exposure to acids and the risk of lung cancer: evidence for specificity of association.

Occupational exposure to strong inorganic acid mists containing sulfuric acid has been recognized as a carcinogen (Group 1) since 1992. An augmented, secondary data analysis of a population-based case-control study of lung cancer was conducted to assess lung cancer-specific risks using 772 lung cancer cases diagnosed between 1981 and 1985. Individually matched controls--on age, gender, and borough of residence--were identified. Lifetime exposure to 10 acidic agents, including strong inorganic acids and some gases, was assessed from complete lifetime occupational histories in terms of concentration, frequency, and reliability of the various exposure assessments. Smoking-adjusted odds ratios and 95% confidence intervals were determined for overall and histology-categorized lung cancers using conditional logistic regression. No excess risk for overall lung cancer was associated with any of the acids, and effect modification by gender could not be identified. The absence of an acid lung cancer effect reinforces more recent toxicological data that suggest specificity to the larynx.

Maternal exposure to occupational solvents and childhood leukemia.

Many organic solvents are considered probable carcinogens. We carried out a population-based case-control study including 790 incident cases of childhood acute lymphoblastic leukemia and as many healthy controls, matched on age and sex. Maternal occupational exposure to solvents before and during pregnancy was estimated using the expert method, which involves chemists coding each individual's job for specific contaminants. Home exposure to solvents was also evaluated. The frequency of exposure to specific agents or mixtures was generally low. Results were generally similar for the period ranging from 2 years before pregnancy up to birth and for the pregnancy period alone. For the former period, the odds ratio (OR), adjusted for maternal age and sex, for any exposure to all solvents together was 1.11 [95% confidence interval (CI), 0.88-1.40]. Increased risks were observed for specific exposures, such as to 1,1,1-trichloroethane (OR = 7.55; 95% CI, 0.92-61.97), toluene (OR = 1.88; 95% CI, 1.01-3.47), and mineral spirits (OR = 1.82; 95% CI, 1.05-3.14). There were stronger indications of moderately increased risks associated with exposure to alkanes (C5-C17; OR = 1.78; 95% CI, 1.11-2.86) and mononuclear aromatic hydrocarbons (OR = 1.64; 95% CI, 1.12-2.41). Risk did not increase with increasing exposure, except for alkanes, where a significant trend (p = 0.04) was observed. Home exposure was not associated with increased risk. Using an elaborate exposure coding method, this study shows that maternal exposure to solvents in the workplace does not seem to play a major role in childhood leukemia.

Listing occupational carcinogens.

The occupational environment has been a most fruitful one for investigating the etiology of human cancer. Many recognized human carcinogens are occupational carcinogens. There is a large volume of epidemiologic and experimental data concerning cancer risks in different work environments. It is important to synthesize this information for both scientific and public health purposes. Various organizations and individuals have published lists of occupational carcinogens. However, such lists have been limited by unclear criteria for which recognized carcinogens should be considered occupational carcinogens, and by inconsistent and incomplete information on the occupations and industries in which the carcinogenic substances may be found and on their target sites of cancer. Based largely on the evaluations published by the International Agency for Research on Cancer, and augmented with additional information, the present article represents an attempt to summarize, in tabular form, current knowledge on occupational carcinogens, the occupations and industries in which they are found, and their target organs. We have considered 28 agents as definite occupational carcinogens, 27 agents as probable occupational carcinogens, and 113 agents as possible occupational carcinogens. These tables should be useful for regulatory or preventive purposes and for scientific purposes in research priority setting and in understanding carcinogenesis.

Controlling for potential confounding by occupational exposures.

Occupational exposure is an important potential confounder in air pollution studies because it is plausible that individuals who live in highly polluted areas also work in more polluted environments. While the original investigators made some efforts to control for possible confounding by occupational variables, it was felt that these could be improved upon. The reanalysis team attempted to control for occupational confounding by supplementing the original data sets with two new variables, an indicator of the "dirtiness" of a subject's job and an indicator of possible exposure to occupational lung carcinogens. The attribution of these variables was based on the job title recorded by the original investigators and on the judgment of our experts concerning typical exposure patterns in different occupations. We fitted Cox proportional-hazards models identical to those that had been used by the original investigators while also including one or both of the new occupational covariates in the models. In none of the analyses did the inclusion of the occupational variables materially change the results. It would therefore appear that, in general, the results reported by the original investigators were not distorted by inadequate control of occupational variables. We also carried out some analyses using the dirtiness index as a stratification variable to assess effect modification. There was some indication, albeit inconsistent, that the effect of air pollution on mortality was greater among subjects with dirty jobs than among those with clean jobs.

Mortality in an Australian cohort of textile workers.

BACKGROUND: Workers in the textile industry may be exposed to textile dusts, a wide range of chemicals and electromagnetic radiation. AIM: To investigate the risk of mortality in a cohort of textile workers and examine whether specific occupational exposures were associated with mortality. METHOD: Data on members and former members of a textile industry union were extracted from membership cards and matched with the National Death Index to obtain date and cause of death. Exposure to 31 different substances was assessed using a specifically designed job exposure matrix that consisted of profiles of exposures in 11 occupational titles. These profiles were modified according to individual circumstances. Standardized mortality ratios (SMRs) were computed comparing the cohort to the Australian population and Mantel-Haenszel estimates of the rate ratios were computed comparing exposed with unexposed for each of the substances. RESULTS: There were 113 deaths in the cohort of 7684 workers. Male and female textile workers had similar risks of death from any cause, cancer or cardiovascular disease to the general Australian population. Male workers had an increased risk of death from injury (SMR = 157, 95% confidence interval 113-213). There were no statistically significant increases in risk with particular occupational exposures. CONCLUSION: Male textile workers are at higher risk of death from injury.

Validation of expert assessment of occupational exposures.

BACKGROUND: Assessment by experts may be the best method available for retrospective occupational exposure measurement in community-based studies. This study was undertaken to examine the validity of occupational exposure assessment by comparing the ratings of experienced raters with previously recorded industrial hygiene measurements. METHODS: We obtained 50 measurements from industrial hygiene records, covering a variety of jobs and substances and created 47 job descriptions around these measurements. Three raters were asked to assess exposure to a checklist of 19 substances (including those substances which had been measured). We estimated the sensitivity of the raters in correctly detecting those substances known to have been present. RESULTS: Using a liberal criterion for the ratings, the average sensitivity among the raters was 90%. Using a more stringent criterion, the average sensitivity was 73%. Among substances coded as present, the raters were quite accurate in rating the relative concentration and frequency of exposure. CONCLUSIONS: This trial demonstrated that a team of experienced raters could successfully characterize jobs in which important exposures occurred.

Occupational exposures to extremely low frequency magnetic fields and postmenopausal breast cancer.

BACKGROUND: The association between occupational exposure to extremely low frequency magnetic fields (ELF-MF) and risk of postmenopausal breast cancer was assessed in a case-control study. METHODS: Breast cancer cases were compared to cancer controls. Interviewers elicited information on risk factors and on lifetime work history. Industrial hygienists assigned to each job average duration of exposure to ELF-MF at four levels of intensities ("none," <0.2 microT; "low," 0.2-<0.5microT; "medium," 0.5-<1microT; "high," > or =1-10microT). Unconditional logistic regression was used to estimate adjusted odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: A total number of 608 cases and 667 controls participated. Adjusting for accepted breast cancer risk factors, we found an OR of 1.13 for lifetime occupational exposure to ELF-MF at medium or high intensities. Risks were larger for exposures before age 35 (OR = 1.40), and statistically significant for exposures before 35 among cases with progesterone receptor positive tumors (OR = 1.56, 95% CI=1.02-2.39). CONCLUSIONS: There appears to be a small increased risk for breast cancer among postmenopausal women exposed occupationally to ELF-MF.