Radiological abnormalities among sheet-metal workers in the construction industry in the United States and Canada: relationship to asbestos exposure

Change in prevalence of asbestos-related disease among sheet metal workers 1986 to 2016

BACKGROUND

A medical screening program began in 1986 for sheet metal workers exposed to asbestos, primarily while working alongside insulators applying spray-on asbestos materials, a practice banned in 1973. Exposure continues during maintenance, renovation, and repair.

METHODS

Radiographic abnormalities among 26 397 sheet metal workers examined from 1986 to 2016 were analyzed by year of entry into the trade. Logistic regression was used to examine risk factors for parenchymal and pleural abnormalities among the overall study population and among the subcohort who entered the trade after 1973.

RESULTS

Prevalence of parenchymal disease was 17.4% for those starting work before 1950 compared with 0.8% for those starting work after 1973 (adjusted prevalence odds ratio [pOR] = 26.65, 95% confidence interval [CI] = 18.46-38.46). For each calendar year after 1973, entering the trade 1 year later was associated with an estimated 12.7% decreased odds of acquiring asbestos-related disease (adjusted pOR = 0.873, 95% CI = 0.832-0.916).

CONCLUSION

Sheet metal workers who began work after the US implemented environmental and occupational regulations develop asbestos-related disease at much reduced rates, consistent with regulatory projections made for nonmalignant asbestos-related disease by the Occupational Safety and Health Administration at the time. Cancer remains a concern among this cohort, and lung cancer screening recommendations should consider year of entry into the trade. This study highlights the importance of regulatory intervention and of continued surveillance.

Comparative Risks of Cancer from Drywall Finishing Based on Stochastic Modeling of Cumulative Exposures to Respirable Dusts and Chrysotile Asbestos Fibers

Sanding joint compounds is a dusty activity and exposures are not well characterized. Until the mid 1970s, asbestos-containing joint compounds were used by some people such that sanding could emit dust and asbestos fibers. We estimated the distribution of 8-h TWA concentrations and cumulative exposures to respirable dusts and chrysotile asbestos fibers for four worker groups: (1) drywall specialists, (2) generalists, (3) tradespersons who are bystanders to drywall finishing, and (4) do-it-yourselfers (DIYers). Data collected through a survey of experienced contractors, direct field observations, and literature were used to develop prototypical exposure scenarios for each worker group. To these exposure scenarios, we applied a previously developed semi-empirical mathematical model that predicts area as well as personal breathing zone respirable dust concentrations. An empirical factor was used to estimate chrysotile fiber concentrations from respirable dust concentrations. On a task basis, we found mean 8-h TWA concentrations of respirable dust and chrysotile fibers are numerically highest for specialists, followed by generalists, DIYers, and bystander tradespersons; these concentrations are estimated to be in excess of the respective current but not historical Threshold Limit Values. Due to differences in frequency of activities, annual cumulative exposures are highest for specialists, followed by generalists, bystander tradespersons, and DIYers. Cumulative exposure estimates for chrysotile fibers from drywall finishing are expected to result in few, if any, mesothelioma or excess lung cancer deaths according to recently published risk assessments. Given the dustiness of drywall finishing, we recommend diligence in the use of readily available source controls.

Mortality among sheet metal workers participating in a respiratory screening program

BACKGROUND

The Sheet Metal Occupational Health Institute Trust (SMOHIT) established a screening program in 1985 to examine the health hazards of the sheet metal industry in the U.S. and Canada.

METHODS

17,345 individuals with over 20 years in the trade and who participated in the program were followed for causes of death between 1986 and 2010. Both SMRs and Cox proportional hazards models investigated predictors of death due to lung cancer, mesothelioma, and chronic obstructive pulmonary disease (COPD).

RESULTS

Significant excess mortality was seen for mesothelioma and asbestosis. Controlling for smoking, a strong trend for increasing lung cancer risk with increasing chest x-ray profusion >0/0 was observed. With an profusion score <1/0, FEV1 /FVC <80% was associated with lung cancer risk. COPD risk increased with increasing profusion score.

CONCLUSIONS

This study demonstrates asbestos-related diseases among workers with largely indirect exposures and an increased lung cancer risk with low ILO scores.

Asbestos-related disease among sheet metal workers 1986-2004: radiographic changes over time

BACKGROUND

In 1985, the Sheet Metal Workers International Association and the Sheet Metal and Air Conditioning National Association formed The Sheet Metal Occupational Health Institute Trust (SMOHIT) to examine the health hazards of the sheet metal industry. Between 1986 and 2004 18,211 individuals were examined. At the time of the first examination 9.6% of all participants (1,745) had findings consistent with parenchymal disease (ILO > 1/0), and 21% (3,827) had pleural scarring.

METHODS

2181-Two thousand hundred eighty-one who had no radiographic evidence of pneumoconiosis on baseline examination underwent a second examination.

RESULTS

By the second examination, 5.3% had developed parenchymal disease on chest radiograph; an additional 12.4% had developed pleural scarring without parenchymal disease. Factors that predicted new cases of pneumoconiosis on radiograph were the calendar year the worker entered the sheet metal trade, smoking, and shipyard work. Forty-seven percent of those smoking at the time of initial exam reported having quit smoking by the second examination.

CONCLUSIONS

Asbestosis is still occurring 50 years after first exposure. Exposed workers benefit from medical screening programs that incorporate smoking cessation.

Change in Prevalence of Asbestos-Related Disease Among Sheet Metal Workers 1986 to 2004

In 1985, the Sheet Metal Workers International Association and the Sheet Metal and Air Conditioning National Association formed The Sheet Metal Occupational Health Institute Trust to examine the health hazards of the sheet metal industry in the United States and Canada. Between 1986 and 2004, 18,211 individuals were examined. The mean age of this cohort was 57.9 years, and the participants had worked for a mean (+/- SD) duration of 32.9 +/- 6 years in the sheet metal trade. Twenty-three percent of participants were current smokers, 49% were former smokers, and 28% were never-smokers. A total of 9.6% of participants (1,745 participants) had findings that were consistent with parenchymal disease (International Labor Organization [ILO] score, >/= 1/0); 60% of those with an ILO score >/= 1/0 were classified as 1/0, 34% as 1/1 to 1/2, and 6% as >/= 2/1. A total of 21% of participants (3,827 participants) had pleural scarring. There was a lower prevalence of nonmalignant asbestos-related disease among those who began to work after 1970, when compared to workers who began to work before 1949; those who began to work between 1950 and 1969 had a prevalence between the other two groups. The strongest predictor of both parenchymal and pleural disease on a chest radiograph was the calendar year in which the worker began sheet metal work; work in a shipyard was also an important risk. The results of this study suggest that the efforts to reduce asbestos exposure in the 1980s through strengthened Occupational Safety and Health Administration regulation have had a positive public health impact.

Asbestos-related pleural diseases: dimensional criteria are not appropriate to differentiate diffuse pleural thickening from pleural plaques

BACKGROUND

In the literature, the criteria used to define pleural plaques (PP) and diffuse pleural thickening (DPT) are very heterogeneous and often imprecise. A multicenter restropective study was conducted to assess the relevance of two radiographic definitions of DPT.

METHODS

The study population consisted of 287 subjects with asbestos-related pleural thickening. Two definitions were used to characterize DPT on postero-anterior chest radiographs: definition 1: pleural thickening associated with obliteration of the costophrenic angle; definition 2: pleural thickening at least 5 mm wide, extending for more than one quarter of the chest wall. Prevalence of respiratory symptoms and pulmonary function tests were compared in the DPT and PP groups resulting from the two definitions of DPT.

RESULTS

According to definition 1, 34 patients (11.8%) were classified in the DPT group. Prevalence of chronic sputum, dyspnea, and chest pain was significantly higher in this group than in the PP group. FEV(1), FVC, and TLC were significantly lower. The differences persisted after adjustment for confounding factors. According to definition 2,102 patients (36.6%) were classified in the DPT group. DPT and PP groups did not differ in terms of prevalence of respiratory symptoms, or pulmonary function tests. Agreement between readers was significantly better when using definition 1.

CONCLUSIONS

Obliteration of costophrenic angle is a much more reliable sign than dimensional criteria to characterize DPT.

Current controversies regarding the role of asbestos exposure in the causation of malignant mesothelioma: the need for an evidence-based approach to develop medicolegal guidelines

Asbestos is a group of fibrous silicate minerals that includes two mineralogic groups: amphiboles and serpentines. While the carcinogenic role of amphiboles (eg, crocidolite and amosite) is well established, medical "experts" that tend to strongly advocate their views currently argue in medicolegal cases multiple specific issues regarding the carcinogenicity of asbestos fibers. For example, it is controversial whether chrysotile causes malignant mesothelioma (MM); what are the specific carcinogenic thresholds for amphiboles and chrysotile; what occupations are truly at risk to develop MM as a result of asbestos exposure; what is the role of chrysotile in the development of peritoneal MM; how to assign causation in individuals exposed to multiple industrial products containing variable concentrations of various asbestos fibers; and, what criteria should be used to accept causation in household exposure cases and others. The causation criteria currently acceptable in U.S. courts are surprisingly flexible and subject to variable interpretation by medical "experts." At a time where thousands of individuals are claiming causation of MM by asbestos exposure, there is a need to develop more specific causation guidelines based on scientific evidence. Evidence-based medicine has been proposed as a new approach to the study, teaching, and the practice of medicine and has been used as a process of systematically reviewing the relevant studies in the literature to assess their scientific validity and development of guidelines. This article summarizes some of the current controversies regarding the role of asbestos exposure in the causation of MM and suggests the need for future evidence-based medicine-type studies to develop causation guidelines that could be used consistently during litigation.

Surveillance of respiratory diseases among construction and trade workers at Department of Energy nuclear sites

BACKGROUND

Medical screening programs were begun in 1996 and 1997 at three Department of Energy (DOE) nuclear weapons facilities (Hanford Nuclear Reservation, Oak Ridge, and the Savannah River Site) to evaluate whether current and former construction workers are at significant risk for occupational illnesses. The focus of this report is pneumoconiosis associated with exposures to asbestos and silica among workers enrolled in the screening programs through September 30, 2001.

METHODS

Workers provided a detailed work and exposure history and underwent a respiratory examination, which included a respiratory history and symptom questionnaire, a posterior-anterior (P-A) chest radiograph, and spirometry. Both stratified and multivariate logistic regression analyses were used to explore the risk of disease by duration of DOE employment and frequency of exposure, while controlling for potential confounders such as age, race, sex, and other work in the construction and building trades.

RESULTS

Of the 2602 workers, 25.2% showed one or more chest X-ray changes by ILO criteria and 42.7% demonstrated one or more pulmonary function defects. The overall prevalence of parenchymal changes by ILO criteria (profusion 1/0 or greater) was 5.4%. In the logistic regression models, the odds ratio for parenchymal disease was 2.6 (95% confidence interval (CI) = 1.0-6.6) for workers employed 6 to 20 years at Hanford or Savannah River and increased to 3.6 (95% CI = 1.1-11.6) for workers employed more than 35 years, with additional incremental risks for workers reporting routine exposures to asbestos or silica.

CONCLUSIONS

Continued surveillance of workers is important given their increased risk of disease progression and their risk for asbestos related malignancies. Smoking cessation programs should also be high priority and continued abstinence for former smokers reinforced. Although the observed respiratory disease patterns are largely reflective of past exposures, these findings suggest that DOE needs to continue to review industrial hygiene control programs for work tasks involving maintenance, repair, renovation, and demolition.

Clinical predictors of mortality from asbestosis in the North American Insulator Cohort, 1981 to 1991

Recorded mortality from asbestosis has increased markedly in the United States in recent decades, from 0.49 to 3.06 per million persons between 1970 and 1990. Although asbestosis is generally considered to be a slowly progressive disorder, little is known about how clinical and exposure parameters among individuals with asbestosis quantitatively predict subsequent risk of death from asbestosis. We followed 2,609 insulators from the North American insulator cohort 10 yr to determine cause of death and to relate clinical findings to risk of death. This group had undergone clinical and radiologic examination between 1981 and 1983 in 19 cities in the United States. Seventy-four (11.0%) of 674 deaths during the subsequent 10 yr were due to asbestosis, according to the best clinical and radiologic evidence available at the time of death. The 10 yr risk of death (expressed as a percentage) due to asbestosis rose sharply with increasing interstitial fibrosis as identified on the baseline chest X-ray, from 0.9% to 2.4%, 10.8%, and 35.4% for International Labor Office (ILO) profusion categories 0, 1, 2, and 3, respectively. Dyspnea, a low FVC, and/or physical examination findings typical of interstitial fibrosis (rales, clubbing, or cyanosis) raised the risk of subsequent death from asbestosis by 2- to 6-fold. The effect of cigarette smoking on risk of death from asbestosis was small and disappeared after adjustment for ILO profusion score.

Relation of spirometric function to radiographic interstitial fibrosis in two large workforces exposed to asbestos: an evaluation of the ILO profusion score

OBJECTIVES

To analyse quantitatively the relations of spirometric lung function (forced vital capacity (FVC)) to radiographic interstitial pulmonary fibrosis (assessed by the International Labour Organisation (ILO) profusion score of small irregular opacities) in two large workforces exposed to different intensities of asbestos. These analyses consider the question whether a similar profusion score n differently exposed workers is associated with a similar effect on lung function.

METHODS

Surveys of two workforces, insulators (n = 2611) and sheet metal workers (n = 1245), by the same investigators allowed comparison of the effects of the two levels of exposure to asbestos. The two groups were of similar age and had similar percentages of non-smokers and smokers. All radiographs were read by the same expert reader.

RESULTS

Consistent with their less continuous and less intense exposure to asbestos, metal workers had: (a) far less frequent radiographic asbestosis (profusion score > or = 1/0, 17.5% v 59.6% for insulators): (b) less severe radiographic asbestosis (only 1.1% had scores > or = 2/1 v 13.3% of insulators); (c) a similar slope to that seen in insulators for the relation between FVC and profusion score when pleural thickening was absent; (d) less frequent pleural fibrosis (36% v 75%); and (e) less frequent restrictive impairment (23% v 33%). In both insulators and metal workers, lung function was below normal even when lung fields were normal, FVG fell with increasing profusion, it was lower in smokers and in those with pleural thickening at comparable profusion scores, and these was no difference in FVC between scores 0/1 and 1/0.

CONCLUSION

The decrease in FVC with increasing profusion score in both workforces as well as the similar slopes for the relation between FVG and profusion score and the similar FVG at similar scores in the absence of pleural thickening confirm the ILO profusion score as an acceptable assessment of pulmonary fibrosis.

Asbestos-related diseases in construction carpenters

To assess the association of minimal parenchymal fibrosis and pleural plaques with respiratory functional impairment, we conducted a survey of 631 asbestos-exposed construction carpenters. This population had a relatively low prevalence of radiographic abnormalities and lung function impairment. Pleural plaques was the asbestos-related disease most prevalent, followed by interstitial fibrosis with predominantly low profusion scores. The most frequent functional impairment was the obstructive pattern, followed by restrictive and mixed patterns. After adjusting for potential confounders, the presence of pleural plaques was significantly associated with a mixed respiratory pattern of impairment (OR = 3.7, 95% CI 1.4-12.3). Furthermore, our data were consistent with a weak association between pleural plaques and a predominantly restrictive defect (OR-1.3, 95% CI 0.4-3.9). This study also suggested an association between minimally detectable profusions and both obstructive (OR = 1.9, 95% CI 0.6-6.3) and mixed (OR = 1.6, 95% CI 0.3-7.1) defects. Although only 631 of a potential 7,649 active and retired union members participated in this first-time survey and were relatively young, these findings add new evidence to the functional importance of pleural fibrosis and minimal parenchymal fibrosis.

The National Sheet Metal Worker Asbestos Disease Screening Program: radiologic findings. National Sheet Metal Examination Group

This report presents data gathered from a series of asbestos disease screening examinations of 9,605 United States sheet metal workers who were first employed in the trade at least 20 years before the examination. The overall prevalence of asbestos-related radiographic changes was 31.1%: 18.8% had pleural abnormalities alone, 6.6% had parenchymal abnormalities (International Labour Office (ILO) score of 1/0 or higher) alone, and 5.7% had both. Among those with 40 years or more since entering the trade, 41.5% had radiographic signs of asbestos-related disease, 24.2% pleural alone, 7.7% parenchymal alone, and 9.6% both pleural and parenchymal abnormalities. After controlling for several surrogates for asbestos exposure level, cigarette smoking was found to increase risk of parenchymal, and more modestly, pleural abnormalities. Each pack-year was associated with a 1% increased prevalence odds ratios for parenchymal abnormalities (ILO category 1 compared to category 0), and 0.4% increased prevalence odds ratios for pleural abnormalities. A history of shipyard employment also produced significantly increased prevalence odds ratios for each radiographic category. More that 90% of chest radiographs were classified by A or B readers; after adjustment for other risk factors, A readers were more likely to report parenchymal abnormalities of category 1, but not more likely to report category 2 or pleural abnormalities, than B readers.