Effect of different approaches to treatment of smoking as a potential confounder in a case-control study on occupational exposures

Methodological issues in descriptive environmental epidemiology. The example of study Sentieri

BACKGROUND

Descriptive epidemiology identifies associations between environmental exposures and health effects that require results from methodologically stronger studies before causation can be considered.

OBJECTIVE

To critically review the methodology and results of Sentieri, a descripitive study on residence in areas with one or more industrial source of pollution.

METHODS

We systematically reviewed the literature quoted by Sentieri for the selection of health effects of nine types of pollution sources of a-priori interest. We also reviewed and meta-analyzed the results of the first report of Sentieri, that analyzed mortality in 44 polluted sites (PS), and 17 causes of deaths during 1995-2002.

RESULTS

Among 159 study results quoted by Sentieri, 23.9 % were supportive of an association between residence near a pollution source and a health effect, 30.2 % were partially supportive, 10.7 % were not supportive, and 35.2 % were not relevant. Among 653 standardized mortality ratios for associations between PS-specific pollution sources and causes of death, 14.4% were significantly above 1.02, and 9.0% were significantly below 0.98. Among 48 meta-analysis, seven were significantly above 1.0, including five on exposure to asbestos.

CONCLUSIONS

Sentieri exemplifies the limitations of descriptive environmental epidemiology studies, in which most hypotheses have limited prior support, most results do not show associations, data on potential confounders and other sources of bias are not available. Such studies tend to replicate well-known associations and occasionally can identify critical situations requiring more investigation, but cannot be used to infer causality either in general or in specific circumstances.

Occupational Burden of Chronic Obstructive Pulmonary Disease in the Commonwealth of Independent States: Systematic Review and Meta-Analysis

Background: Population-based studies from the Russian Federation and neighboring countries on the occupational burden of chronic obstructive pulmonary disease (COPD) are seldom or not included in the systematic reviews. The aim of this review was to summarize published population-based studies from the Commonwealth of Independent States (CIS) in order to ascertain the occupational burden of COPD. Methods: We systematically searched www.elibrary.ru and PubMed for population-based studies on the epidemiology of COPD in nine countries using PRISMA. Quality of studies was assessed using the original tool. The odds of COPD in the included studies from vapors, gases, dusts, and fumes (VGDF) was pooled using meta-analysis (fixed effects model), whereas the population attributable fraction percent (PAF%) was pooled with meta-proportion using the random effects model in Stata 14.2. Results: Five studies, three from Russia, one from Kazakhstan, and one more from Azerbaijan and Kazakhstan (total N = 18,908) with moderate to high quality and published from 2014 to 2019 (none from Armenia, Belarus, Kyrgyzstan, Moldova, Tajikistan, and Uzbekistan), were included. Spirometry-defined COPD was the outcome in four of them. The pooled odds ratio (OR) of COPD from VGDF was 1.69 [95% confidence interval (CI) 1.34;2.13], greater in Kazakhstan [OR 1.96 (95% CI 1.35;2.85, N = 2 studies)] compared to Russia [OR 1.52 (95% CI 1.13;2.05, N = 2 studies)]. The pooled PAF% was 6% (95% CI 2; 14%) from three studies. Conclusions: Population-based studies in the CIS get little attention with very few studies published. Although the effect was greater in Kazakhstan compared to Russia, the overall effect did not differ from studies published in the rest of the world. Research capacity to study occupational risks of COPD should be strengthened to produce more evidence of higher quality.

Former Workers of a Bright Electroplating Factory Located in Vercelli: A Cohort Study From 1974 to 2016: Legal Expertise Results

BACKGROUND

The mortality risk among former workers of a factory with an adjoining galvanic activity has been assessed; several environmental analyses found in the site the presence of nickel and organochlorinated substances.

METHODS

The cohort followed by 1974 to 2016 is represented by 899 individuals in which there were 191 deaths: 140 males and 51 females. A risks analysis with elaboration of SMR between observed cases and the expected one referring to Piemonte region rates was performed.

RESULTS

The excesses stratified by gender and task have highlighted enhanced cancer risk (especially lung and liver cancers) among men workers. For females, cancer risk is enhanced especially for pancreas, ovary, and total digestive tract cancers.

CONCLUSION

The report confirms an increased risk between nickel and lung cancers and organochlorinated and liver cancer.

Low radon exposures and lung cancer risk: joint analysis of the Czech, French, and Beaverlodge cohorts of uranium miners

It is well established that high radon exposures increase the risk of lung cancer mortality. The effects of low occupational exposures and the factors that confound and modify this risk are not clear and are needed to inform current radiation protection of miners. The risk of lung cancer mortality at low radon exposures (< 100 working-level months) was assessed in the joint cohort analysis of Czech, French, and Canadian uranium miners, employed in 1953 or later. Statistical analysis was based on linear Poisson regression modeling with grouped cohort survival data. Two sensitivity analyses were used to assess potential confounding from tobacco smoking. A statistically significant linear relationship between radon exposure and lung cancer mortality was found. The excess relative risk per working-level month was 0.022 (95% confidence intervals: 0.013-0.034), based on 408 lung cancer deaths and 394,236 person-years of risk. Time since exposure was a statistically significant modifier; risk decreased with increasing time since exposure. A tendency for a decrease in risk with increasing attained age was observed, but this was not statistically significant. Exposure rate was not found to be a modifier of the excess relative risk. The potential confounding effect of tobacco smoking was estimated to be small and did not substantially change the radon-lung cancer mortality risk estimates. This joint cohort analysis provides strong evidence for an increased risk of lung cancer mortality from low occupational radon exposures. The results suggest that radiation protection measures continue to be important among current uranium miners.

Population Attributable Risk for Occupational Gancer in Italy

Population studies estimating the proportion of cancer attributable to occupation (PAR) in different geographical areas in Italy are reviewed. Studies using lists of industrial activities and occupations which are known or suspected to entail exposure to lung carcinogens gave lung cancer PARs between 5% and 36%. Those using job-exposure matrices estimated PARs of 3%-53%, with most of the values ranging between 17 and 33%. For bladder cancer, PARs ranged between 4% and 24%. The uses and limitations of calculating population attribultable risk are discussed.

Radon, smoking and lung cancer risk: results of a joint analysis of three European case-control studies among uranium miners

A combined analysis of three case-control studies nested in three European uranium miner cohorts was performed to study the joint effects of radon exposure and smoking on lung cancer death risk. Occupational history and exposure data were available from the cohorts. Smoking information was reconstructed using self-administered questionnaires and occupational medical archives. Linear excess relative risk models adjusted for smoking were used to estimate the lung cancer risk associated with radon exposure. The study includes 1046 lung cancer cases and 2492 controls with detailed radon exposure data and smoking status. The ERR/WLM adjusted for smoking is equal to 0.008 (95% CI: 0.004-0.014). Time since exposure is shown to be a major modifier of the relationship between radon exposure and lung cancer risk. Fitting geometric mixture models yielded arguments in favor of a sub-multiplicative interaction between radon and smoking. This combined study is the largest case-control study to investigate the joint effects of radon and smoking on lung cancer risk among miners. The results confirm that the lung carcinogenic effect of radon persists even when smoking is adjusted for, with arguments in favor of a sub-multiplicative interaction between radon and smoking.

Lung cancer and occupation: A New Zealand cancer registry-based case-control study

BACKGROUND

There are many proven and suspected occupational causes of lung cancer, which will become relatively more important over time, as smoking prevalence decreases.

METHODS

We interviewed 457 cases aged 20-75 years notified to the New Zealand Cancer Registry during 2007-2008, and 792 population controls. We collected information on demographic details, potential confounders, and employment history. Associations were estimated using logistic regression adjusted for gender, age, ethnicity, smoking, and socio-economic status.

RESULTS

Among occupations of a priori interest, elevated odds ratios (ORs) were observed for sawmill, wood panel and related wood-processing plant operators (OR 4.63; 95% CI 1.05-20.29), butchers (OR 8.77, 95% CI 1.06-72.55), rubber and plastics products machine operators (4.27; 1.16-15.66), heavy truck drivers (2.24; 1.19-4.21) and workers in petroleum, coal, chemical and associated product manufacturing (1.80; 1.11-2.90); non-significantly elevated risks were also observed for loggers (4.67; 0.81-27.03), welders and flame-cutters (2.50; 0.86-7.25), pressers (5.74; 0.96-34.42), and electric and electronic equipment assemblers (3.61; 0.96-13.57). Several occupations and industries not of a priori interest also showed increased risks, including nursing associate professionals (5.45; 2.29-12.99), enrolled nurses (7.95; 3.10-20.42), care givers (3.47; 1.40-8.59), plant and machine operators and assemblers (1.61; 1.20-2.16), stationary machine operators and assemblers (1.67; 1.22-2.28), food and related products processing machine operators (1.98; 1.23-3.19), laborers and related elementary service workers (1.45; 1.05-2.00), manufacturing (1.34; 1.02-1.77), car retailing (3.08; 1.36-6.94), and road freight transport (3.02; 1.45-6.27).

CONCLUSIONS

Certain occupations and industries have increased lung cancer risks in New Zealand, including wood workers, metal workers, meat workers, textile workers and drivers. Am. J. Ind. Med. 54:89-101, 2011. © 2010 Wiley-Liss, Inc.

Lung cancer and occupation in a population-based case-control study

The authors examined the relation between occupation and lung cancer in the large, population-based Environment And Genetics in Lung cancer Etiology (EAGLE) case-control study. In 2002-2005 in the Lombardy region of northern Italy, 2,100 incident lung cancer cases and 2,120 randomly selected population controls were enrolled. Lifetime occupational histories (industry and job title) were coded by using standard international classifications and were translated into occupations known (list A) or suspected (list B) to be associated with lung cancer. Smoking-adjusted odds ratios and 95% confidence intervals were calculated with logistic regression. For men, an increased risk was found for list A (177 exposed cases and 100 controls; odds ratio = 1.74, 95% confidence interval: 1.27, 2.38) and most occupations therein. No overall excess was found for list B with the exception of filling station attendants and bus and truck drivers (men) and launderers and dry cleaners (women). The authors estimated that 4.9% (95% confidence interval: 2.0, 7.8) of lung cancers in men were attributable to occupation. Among those in other occupations, risk excesses were found for metal workers, barbers and hairdressers, and other motor vehicle drivers. These results indicate that past exposure to occupational carcinogens remains an important determinant of lung cancer occurrence.

Accounting for smoking in the radon-related lung cancer risk among German uranium miners: results of a nested case-control study

The possible confounding effect of smoking on radon-associated risk for lung cancer mortality was investigated in a case-control study nested in the cohort of German uranium miners. The study included 704 miners who died of lung cancer and 1,398 controls matched individually for birth year and attained age. Smoking status was reconstructed from questionnaires and records from the mining company's health archives for 421 cases and 620 controls. Data on radon exposure were taken from a job-exposure matrix. Smoking adjusted odds ratios for lung cancer in relation to cumulative radon exposure have been calculated with conditional logistic regression. The increase in risk per Working Level Month (WLM) was assessed with a linear excess relative risk (ERR) model taking smoking into account as a multiplicative factor. In addition, the potential impact of temporal factors on the ERR per WLM was examined. Lung cancer mortality risk increased with increasing radon exposure, yielding a crude ERR per WLM of 0.25% (95% CI: 0.13-0.46%). Adjustment for smoking led only to marginal changes of the radon-associated lung cancer risks. The adjusted ERR per WLM was very similar (0.23%, 95%-CI: 0.11-0.46%) to the crude risk and to the risk found in the Wismut cohort study. This stability of the radon-related lung cancer risks with and without adjustment for smoking suggests that smoking does not act as a major confounder in this study and presumably also not in the cohort study.

A case-control study on occupational risk factors for sino-nasal cancer

OBJECTIVES

Sino-nasal cancer has been consistently associated with exposure to wood dust, leather dust, nickel and chromium compounds; for other occupational hazards, the findings are somewhat mixed. The aim of this study was to investigate the risk of sino-nasal epithelial cancer (SNEC) by histological type with prior exposure to suspected occupational risk factors and, in particular, those in metalworking.

METHODS

Between 1996 and 2000, incident cases were collected on a monthly basis from hospitals throughout the Piedmont region of Italy by the regional Sino-nasal Cancer Registry. A questionnaire on occupational history, completed by 113 cases and 336 hospital controls, was used to assign exposure to occupational hazards. The relationship between SNEC and cumulative exposure to these hazards was explored using unconditional logistic regression to statistically adjust for age, sex, smoking and co-exposures, allowing for a 10-year latency period.

RESULTS

The risk of adenocarcinoma was significantly increased with ever-exposure to wood dust (odds ratio; OR = 58.6), and to leather dust (OR = 32.8) and organic solvents (OR = 4.3) after controlling for wood dust, whereas ever-exposure to welding fumes (OR = 3.7) and arsenic (OR = 4.4) significantly increased the risk for squamous cell carcinoma. For each of these hazards, a significant increasing trend in risk across ordered cumulative exposure categories was found and, except for arsenic, a significantly increased risk with ever-exposure at low intensity. Treating cumulative exposure on a continuous scale, a significant effect of textile dusts was also observed for adenocarcinoma. For a mixed group of other histological types, a significant association was found with wood dust and organic solvents.

CONCLUSIONS

Some occupational risk factors for SNEC were confirmed, and dose-response relationships were observed for other hazards that merit further investigation. The high risk for adenocarcinoma with low-intensity exposure to wood dust lends support for a reduction in the occupational threshold value.

Occupations and lung cancer: a population-based case-control study in British Columbia

An investigation based on a large population-based case-control study in British Columbia, Canada, was conducted to identify high-risk occupations for lung cancer by histological subtypes. Subjects were 14,755 male incident cancer cases for whom lifetime occupational histories and information on smoking and relevant covariates were collected. Occupational associations for 2998 lung cancer cases, including histological subtypes, were assessed by logistic regression using other cancer cases, excluding smoking-related cancers, as controls. An excess risk of lung cancer was found among workers in metal processing, bakers, and ship deck crew for all histological subtypes, and construction workers, chefs and cooks, and medical workers for specific histological subtypes. Occupational associations that are unique to histological subtypes of lung cancer were identified. Owing to a scarcity of literature in this area, future research needs to focus on confirming these histological associations, and identifying the risk from key exposures found within these occupations (e.g., medical radiation, electromagnetic fields, and cooking fumes).

Shared occupational risks for transitional cell cancer of the bladder and renal pelvis among men and women in Sweden

BACKGROUND

Unlike cancer of the bladder, cancer of the renal pelvis is not considered an occupational cancer and little is known about risks among women.

METHODS

Using the Swedish national census and cancer registry-linked data (1971-1989), we identified transitional cell cancers of the renal pelvis (N = 1,374) and bladder (N = 21,591). Correlation between cancer sites for the standardized incidence ratios (SIR) were determined using Pearson's coefficient of the log SIR. Relative risks of job exposure matrix variables were calculated using Poisson regression.

RESULTS

Both cancer sites were significantly elevated among women and men employed in the machine/electronics industry, sedentary work, and indoor work, and men in the metal industry. The highest proportion of the bladder (12%) and renal pelvis (14%) cancers occurred among men employed in shop and construction metal work. Risks by industry were more correlated among women (r = 0.49, P = 0.002) than men (r = 0.24, P = 0.04). Cancers of the renal pelvis were elevated in several occupational and industry groups for which there was no elevated bladder cancer risk.

CONCLUSION

Cancers of the renal pelvis and bladder share common occupational risk factors that may be more frequent among women. In addition, there may be some jobs that pose an increased risk specifically for cancer of the renal pelvis but not bladder.

Methodological issues regarding confounding and exposure misclassification in epidemiological studies of occupational exposures

BACKGROUND

Confounding and exposure misclassification are issues that concern epidemiologists because of their potential to bias results of studies and complicate interpretations. In occupational epidemiology both are routinely raised to argue that an observed result is either a false positive or a false negative finding. Although it is important to consider the potential for limitations of epidemiologic investigations, judgment regarding their importance should be based on their actual likelihood of occurrence.

METHODS

This paper is based on our experience in epidemiologic analyses and a brief review of the literature regarding confounding and exposure misclassification.

RESULTS

Examples of substantial confounding are rare in occupational epidemiology. In fact, even for studies of occupational exposures and lung cancer, tobacco-adjusted relative risks rarely differ appreciably from the unadjusted estimates. This is surprising because it seems the perfect situation for confounding to occur. Yet, despite the lack of evidence that confounding is a common problem, nearly every epidemiologic paper includes a lengthy discussion on uncontrolled or residual confounding. On the other hand, exposure misclassification probably occurs in all studies. The only question is, how much? The direction and magnitude of nondifferential exposure misclassification (the type most likely to occur in cohort studies) on estimates of relative risks can be largely predicted given knowledge on the degree of misclassification, that is, relatively small amounts of misclassification can bias relative risks substantially towards the null. The literature, however, is full of discussions implying that misclassification of exposure is an explanation for a positive finding.

CONCLUSIONS

These comments are not to suggest that all potential limitations for epidemiologic studies should not be considered and evaluated. We do believe, however, that the likelihood of occurrence and the direction and magnitude of the effect should be more carefully and realistically considered when making judgments about study design or data interpretation.

Bladder cancer risk in sales workers: artefact or cause for concern?

BACKGROUND

A large number of epidemiological studies have reported positive associations between bladder cancer and sales occupations. We investigated whether these findings are likely to be due to chance, confounding or publication bias, or may involve causal associations.

METHODS

Studies reporting bladder cancer risk-estimates for sales occupations were reviewed. Using meta-analyses we assessed heterogeneity and publication bias, and derived summary estimates.

RESULTS

Eighteen publications were identified, reporting 85 risk-estimates for sales-work. Meta-estimates were elevated for men (odds ratio (OR) 1.11, 95% confidence interval (CI) 1.01-1.21) and women (OR = 1.36, 95% CI = 1.11-1.67). The estimate was heterogeneous for men (p(Q-test) <0.01, women: 0.18) and indicated publication bias for women (p(Egger-test) <0.01, men: 0.40). When including only smoking-adjusted estimates reported irrespective of the strength of the association, the summary estimate for generic groups of sales workers was 0.99 (95% CI 0.90-1.08) for men, and 1.18 (95% CI = 0.99-1.39) for women, without statistically significant heterogeneity or publication bias. For women, risk was positively associated with longer duration of sales-employment in three studies.

CONCLUSIONS

Publication bias explained most of the reported increased bladder cancer risk, but sales-work still appeared to be associated with a small risk in women. Possible causal factors include lower frequency of urination and reduced fluid intake.