Comparison of storage phosphor computed radiography with conventional film-screen radiography in the recognition of pneumoconiosis.

Traditional film-screen radiography (FSR) has been useful in the recognition and evaluation of interstitial lung diseases, but is becoming increasingly obsolete. To evaluate the applicability of storage phosphor digital computed radiography (CR) images in the recognition of small lung opacities, we compared image quality and the profusion of small opacities between FSR and CR radiographs. We screened 1,388 working coal miners during the course of the study with FSR and CR images obtained on the same day from all participants. Each traditional chest film was independently interpreted by two of eight experienced readers using the International Labour Office (ILO) classification of radiographs of pneumoconiosis, as were CR images displayed on medical-grade computer monitors. The prevalence of small opacities (ILO category 1/0 or greater) did not differ between the two imaging modalities (5.2% for FSR and 4.8% for soft copy CR; p>0.50). Inter-reader agreement was also similar between FSR and CR. Significant differences between image modalities were observed in the shape of small opacities, and in the proportion of miners demonstrating high opacity profusion (category 2/1 and above). Our results indicate that, with appropriate attention to image acquisition and soft copy display, CR digital radiography can be equivalent to FSR in the identification of small interstitial lung opacities.

Mortality among U.S. underground coal miners: a 23-year follow-up.

BACKGROUND: The mortality experience over 22-24 years of 8,899 working coal miners initially medically examined in 1969-1971 at 31 U.S. coal mines was evaluated. METHODS: A cohort life-table analysis was undertaken on underlying causes of death, and proportional hazards models were fitted to both underlying, and underlying and contributing causes of death. RESULTS: Elevated mortality from nonviolent causes, nonmalignant respiratory disease (NMRD), and accidents was observed, but lung cancer and stomach cancer mortality were not elevated. Smoking, pneumoconiosis, coal rank region, and cumulative coal mine dust exposure were all predictors of mortality from nonviolent causes and NMRD. Mortality from nonviolent causes and NMRD was related to dust exposure within the complete cohort and also for the never smoker subgroup. Dust exposure relative risks for mortality were similar for pneumoconiosis, NMRD, and chronic airways obstruction. CONCLUSIONS: The findings confirm and enlarge upon previous results showing that exposure to coal mine dust leads to increased mortality, even in the absence of smoking.

Rapidly progressive coal workers' pneumoconiosis in the United States: geographic clustering and other factors.

BACKGROUND: Despite significant progress made in reducing dust exposures in underground coal miners in the United States, severe cases of coal workers' pneumoconiosis (CWP), including progressive massive fibrosis (PMF), continue to occur among coal miners. AIMS: To identify US miners with rapidly progressive CWP and to describe their geographic distribution and associated risk factors. METHODS: Radiographic evidence of disease progression was evaluated for underground coal miners examined through US federal chest radiograph surveillance programmes from 1996 to 2002. A case of rapidly progressive CWP was defined as the development of PMF and/or an increase in small opacity profusion greater than one subcategory over five years. County based prevalences were derived for both CWP and rapidly progressive cases. RESULTS: A total of 886 cases of CWP were identified among 29 521 miners examined from 1996 to 2002. Among the subset of 783 miners with CWP for whom progression could be evaluated, 277 (35.4%) were cases of rapidly progressive CWP, including 41 with PMF. Miners with rapidly progressive CWP were younger than miners without rapid progression, were more likely to have worked in smaller mines (<50 employees), and also reported longer mean tenure in jobs involving work at the face of the mine (in contrast to other underground mining jobs), but did not differ with respect to mean underground tenure. There was a clear tendency for the proportion of cases of rapidly progressive CWP to be higher in eastern Kentucky, and western Virginia. CONCLUSIONS: Cases of rapidly progressive CWP can be regarded as sentinel health events, indicating inadequate prevention measures in specific regions. Such events should prompt investigations to identify causal factors and initiate appropriate additional measures to prevent further disease.

Risk of silicosis in cohorts of Chinese tin and tungsten miners, and pottery workers (I): an epidemiological study.

BACKGROUND: Epidemiological evaluations of the risk of silicosis in relation to exposure to crystalline silica have raised the question of whether different types of silica dust exposures vary with respect to their ability to cause silicosis. The aim of this study is to compare the risk of silicosis among cohorts of silica dust-exposed Chinese tin miners, tungsten miners, and pottery workers and to assess whether gravimetric measurements of respirable silica dust sufficiently determine the risk of silicosis or whether other factors of exposure may play a significant role. METHODS: Cohorts were selected from 20 Chinese mines and potteries. Inclusion criteria were starting employment after January 1, 1950 and being employed for at least 1 year during 1960-1974 in one of the selected workplaces. Radiological follow-up for silicosis onset was from January 1, 1950 through December 31, 1994. Silicosis was assessed according to the Chinese radiological criteria for diagnosis of pneumoconiosis (as suspect, Stage I, II, or III). Exposure-response relationships were estimated for silicosis of Stage I or higher. Silica dust exposure was estimated in terms of cumulative total dust exposure, calculated from a workplace, job title, and calendar year exposure matrix, and individual occupational histories. Cumulative total dust exposure was converted in two steps into cumulative respirable dust exposure and cumulative respirable silica dust exposure using conversion factors estimated from side-by-side measurements conducted in 1988-89. RESULTS: The male cohorts included 4,028 tin miners, 14,427 tungsten miners, and 4,547 pottery workers who had similar onset of employment and duration of follow-up. For a given exposure level, the risk of silicosis was higher for the tin and tungsten than the pottery workers. CONCLUSION: The observed differences in the risk of silicosis among the three cohorts suggest that silica dust characteristics, in addition to cumulative respirable silica dust exposure, may affect the risk of silicosis.

Tuberculosis mortality by industry in the United States, 1990-1999.

OBJECTIVE: To identify occupations and industries with elevated respiratory tuberculosis (TB) mortality in the United States for the period 1990-1999, we used National Center for Health Statistics multiple-cause-of-death data, restricted to certain states for which information on decedents' usual industry and occupational information was available and limited to US residents aged > or =15 years. DESIGN: A total of 7686 deaths between 1990 and 1999 were attributed to respiratory TB. Proportionate mortality ratios (PMRs), adjusted for age, sex, and race, were calculated from US census occupation and industry classifications. RESULTS: Industries and occupations involving potential contact with infected cases (e.g., health care workers), those with silica exposure and silicosis (e.g., mining and construction), and those associated with low socioeconomic status had significantly elevated TB mortality. CONCLUSIONS: Overall, the pattern of findings echoes that described in various prior reports, which indicates that the potential for exposure and disease development still persists among certain worker groups. The findings should be useful in guiding occupationally targeted TB prevention programs.

Building-related respiratory symptoms can be predicted with semi-quantitative indices of exposure to dampness and mold.

UNLABELLED: Using a semi-quantitative mold exposure index, the National Institute for Occupational Safety and Health (NIOSH) investigated 13 college buildings to examine whether building-related respiratory symptoms among employees are associated with environmental exposure to mold and dampness in buildings. We collected data on upper and lower respiratory symptoms and their building-relatedness, and time spent in specific rooms with a self-administered questionnaires. Trained NIOSH industrial hygienists classified rooms for water stains, visible mold, mold odor, and moisture using semi-quantitative scales and then estimated individual exposure indices weighted by the time spent in specific rooms. The semi-quantitative exposure indices significantly predicted building-related respiratory symptoms, including wheeze [odds ratio (OR) = 2.3; 95% confidence interval (CI) = 1.1-4.5], chest tightness (OR = 2.2; 95% CI = 1.1-4.6), shortness of breath (OR = 2.7; 95% CI = 1.2-6.1), nasal (OR = 2.5; 95% CI = 1.3-4.7) and sinus (OR = 2.2; 95% CI = 1.2-4.1) symptoms, with exposure-response relationships. We found that conditions suggestive of indoor mold exposure at work were associated with building-related respiratory symptoms. Our findings suggest that observational semi-quantitative indices of exposure to dampness and mold can support action to prevent building-related respiratory diseases. PRACTICAL IMPLICATIONS: Current air sampling methods have major limitations in assessing exposure to mold and other biological agents that may prevent the demonstration of associations of bioaerosol exposure with health. Our study demonstrates that semi-quantitative dampness/mold exposure indices, based solely on visual and olfactory observation and weighted by time spent in specific rooms, can predict existence of excessive building-related respiratory symptoms and diseases. Relative extent of water stains, visible mold, mold odor, or moisture can be used to prioritize remediation to reduce potential risk of building-related respiratory diseases. From a public health perspective, these observational findings justify action to correct water leaks and repair water damage in order to prevent building-related respiratory diseases. This approach can also be a basis for developing practical building-diagnostic tools for water-incursion.

Pulmonary inflammation and crystalline silica in respirable coal mine dust: dose-response.

This study describes the quantitative relationships between early pulmonary responses and the estimated lung-burden or cumulative exposure of respirable-quartz or coal mine dust. Data from a previous bronchoalveolar lavage (BAL) study in coal miners (n = 20) and nonminers (n = 16) were used including cell counts of alveolar macrophages (AMs) and polymorphonuclear leukocytes (PMNs), and the antioxidant superoxide dismutase (SOD) levels. Miners' individual working lifetime particulate exposures were estimated from work histories and mine air sampling data, and quartz lung-burdens were estimated using a lung dosimetry model. Results show that quartz, as either cumulative exposure or estimated lung-burden, was a highly statistically significant predictor of PMN response (P < 0.0001); however cumulative coal dust exposure did not significantly add to the prediction of PMNs (P = 0.2) above that predicted by cumulative quartz exposure (P < 0.0001). Despite the small study size, radiographic category was also significantly related to increasing levels of both PMNs and quartz lung burden (P-values < 0.04). SOD in BAL fluid rose linearly with quartz lung burden (P < 0.01), but AM count in BAL fluid did not (P > 0.4). This study demonstrates dose-response relationships between respirable crystalline silica in coal mine dust and pulmonary inflammation, antioxidant production, and radiographic small opacities.

Exposure to silica and silicosis among tin miners in China: exposure-response analyses and risk assessment.

OBJECTIVES: To investigate the risk of silicosis among tin miners and to investigate the relation between silicosis and cumulative exposure to dust (Chinese total dust and respirable crystalline silica dust). METHODS: A cohort study of 3010 miners exposed to silica dust and employed for at least 1 year during 1960-5 in any of four Chinese tin mines was conducted. Historical total dust data from China were used to create a job exposure matrix for facility, job title, and calendar year. The total dust exposure data from China were converted to estimates of exposure to respirable crystalline silica for comparison with findings from other epidemiological studies of silicosis. Each worker's work history was abstracted from the complete employment records in mine files. Diagnoses of silicosis were based on 1986 Chinese pneumoconiosis Roentgen diagnostic criteria, which classified silicosis as stages I-III-similar to an International Labour Organisation (ILO) classification of 1/1 or greater. RESULTS: There were 1015 (33.7%) miners identified with silicosis, who had a mean age of 48.3 years, with a mean of 21.3 years after first exposure (equivalent to 11.0 net years in a dusty job). Among those who had silicosis, 684 miners (67.4%) developed silicosis after exposure ended (a mean of 3.7 years after). The risk of silicosis was strongly related to cumulative exposure to silica dust and was well fitted by the Weibull distribution, with the risk of silicosis less than 0.1% when the Chinese measure of cumulative exposure to total dust (CTD) was under 10 mg/m(3)-years (or 0.36 mg/m(3)-years of respirable crystalline silica), increasing to 68.7% when CTD exposure was 150 mg/m(3)-years (or 5.4 mg/m(3)-years of respirable crystalline silica). Latency period was not correlated to the risk of silicosis or cumulative dose of exposure. This study predicts about a 36% cumulative risk of silicosis for a 45 year lifetime exposure to these tin mine dusts at the CTD exposure standard of 2 mg/m(3), and a 55% risk at 45 years exposure to the current United States Occupational Safety and Health Administration and Mine Safety and Health Administration standards of 0.1 mg/m(3) 100% respirable crystalline silica dust. CONCLUSIONS: A clear exposure-response relation was detected for silicosis in Chinese tin miners. The study results were similar to most, but not all, findings from other large scale exposure-response studies.

Regression method to estimate provisional TLV/WEEL-equivalents for non-carcinogens.

There is a huge and changing number of chemicals in commerce for which workplace exposure criteria have not been assigned. Assigning an exposure criterion by an expert committee is resource-intensive-not soon available for the large majority of chemicals in current use. In the absence of assigned criteria, we have provided a regression method to estimate a first-screen estimate of a 'TLV/WEEL-equivalent' inhalation time-weighted average exposure criterion for a pure chemical (or chemical group) from a measure of a non-stochastic toxic exposure to elicit a chronic or sub-chronic health effect, known as a lowest observable adverse effect level (LOAEL) or a (highest) no observable adverse effect level (NOAEL). Results are presented for six data sets for which both a threshold limit value (TLV) or workplace environmental exposure level (WEEL) exposure criterion is presently assigned, and a LOAEL or NOAEL measure of toxic health effect was available from the United States Environmental Protection Agency Integrated Risk Information System data base. The results can be applied as a first estimate of exposure to substances for which no TLV or WEEL (TLV/WEEL) exists, and also serve as a mechanism for identifying substances for potential re-evaluation of their exposure limit, based on their relative position about the prediction models.

Effect of different grouping strategies in developing estimates of personal exposures: specificity versus precision.

There has been increasing interest in recent years in developing strategies in epidemiology for the summarization of occupational exposures, strategies that serve to clarify observed relationships between occupational exposure and health outcomes. Where source occupational exposure data are scarce, it is common to assemble exposure groups with the goal of increasing the extent to which data-based exposure estimates are available for an entire cohort. There has been little guidance, however, on the effect of different grouping strategies on the observed fit between exposure and health outcome. This investigation examined the effect of the use of different exposure summarization strategies on observed relationships between dust exposure and lung function decline among coal mine workers. The dust exposure and spirometry data employed were gathered in the National Study of Coalworkers' Pneumoconiosis. An analysis of variance procedure was carried out to characterize the variability of the dust exposure data, employing single variables relating to mine identity, occupation, and year, as well as two- and three-way multivariate combinations of these variables. The resulting combinations were ranked according to the standard deviation of the observed exposure range to reflect the relative specificity of the various approaches. Sequential arrangements of single- and multiple-variable combinations were constructed, alternately employing highly specific codes or broad categories for mine, occupation, and year. Annual exposure estimates were constructed on the basis of these sequences and used in tandem with longitudinal change in forced expiratory volume (FEV1) in linear multiple regression procedures. Height, age, smoking status, and dust exposure were employed as predictor variables. The results show that the use of broad categorization approaches had a substantial impact on observed regression coefficients. The largest change was observed for categorization according to occupation, which resulted in two- to three-fold increases in the magnitude of observed regression coefficients. These results suggest that the use of highly specific exposure summarization approaches may result in regression outcomes which are marked by a high degree of attenuation, and that consideration of the precision of summarized exposure estimates is an important component of an effective exposure assessment strategy.

Reliability of reported occupational history information for US coal miners, 1969-1977.

For estimating reliable exposure-response relations it is necessary that random variation in both the response and the exposure variables be sufficiently small. Variability in cumulative exposures can arise from uncertainties in self-reported work histories from interviews. In most epidemiologic surveys, the information gathered from questionnaires is used without knowing the validity or reproducibility of these data. This paper investigates the reliability of occupational histories reported by the same individuals on two occasions separated by 9 years in the US National Study of Coal Workers' Pneumoconiosis and its implications on the exposure-response relation for simple coal workers' pneumoconiosis. For 480 coal miners, from whom occupational histories were obtained twice (in 1969-1971 and 1977-1981), the reliability (intraclass correlation coefficient) of the cumulative exposures generated from each work history was 87%. Logistic model fitting of simple coal workers' pneumoconiosis prevalence to the cumulative coal dust exposure produced almost identical results. After accounting for intersurvey variability in the occupational histories, the authors found that the exposure-response coefficients estimated from information reported at the surveys were attenuated by 12%. In epidemiologic studies, knowledge of the reproducibility of self-reported occupational history information is important to ascertain whether the true exposure effect is underestimated.

Respiratory symptoms and spirometry in experienced coal miners: effects of both distant and recent coal mine dust exposures.

The goal of this study was to determine whether respiratory symptoms were associated with the lower concentrations of respirable coal mine dust that were required by the U.S. Coal Mine Health and Safety Act (CMHSA) of 1969. The subjects were 1,866 male miners who had participated in the National Study of Coal Workers' Pneumoconiosis (NSCWP) and been tested at least twice, initially in either Round 1 (R1) (1969-71) or Round 2 (R2) (1972-75) and then finally in Round 4 (R4) (1985-88). Self-reported information elicited with a standardized questionnaire was used to determine the presence at the final round (i.e., R4) of chronic bronchitis, shortness of breath, and wheeze. Cumulative coal mine dust exposure was characterized for both the pre- and post-CMHSA periods. Controlling for age and other potential confounders, increased risks for the symptoms were associated with higher levels of both measurements of exposure. Moreover, the adverse effects of the lower, post-CMHSA exposure were evident for shortness of breath and wheeze especially among subjects who had little pre-CMHSA coal mining experience. These findings provide additional evidence of the limitations of the current 2.0 mg/m3 coal mine dust standard to prevent respiratory disease.

Radiographic and pathologic correlation of coal workers' pneumoconiosis.

The relationships between chest radiographs (CXR) and corresponding pathology were investigated in 430 autopsied coal miners from West Virginia. Whole-lung sections were reviewed and graded on four-point severity scales for the following lesions of coal workers' pneumoconiosis (CWP): macules, micro- and macronodules (small and large fibrotic nodules), and progressive massive fibrosis (PMF). Antemortem CXR were classified by three B readers using the 1971 International Labor Office (ILO) U/C classification (6). On pathologic examination, 96% of miners had macules, 70% micronodules, 45% macronodules, 15% silicosis, and 28% PMF. By CXR, 69% of the miners had small, rounded opacity profusions of category > or = 0/1. Data analysis revealed increasing odds that small opacities of category > or = 0/1 would be detected with increasing grade of nodules. Profusion category 0/0 was often reported for cases with macules of mild to moderate grade and mild levels of micronodules. Overall, q-type opacities were associated with macules and micronodules, whereas the large r-type opacities were associated with macronodules. By CXR, large opacities showed good correlation with pathologic PMF. However, about one-third of cases identified as having large opacities by CXR were not substantiated as PMF by pathology. One-fourth of these cases could be explained by lung lesions such as Caplan's nodules, tuberculosis scars, and tumors. Similarly, 22% of cases classified as PMF on pathology had no large opacities by CXR. In half of these cases, the radiologists had noted other abnormalities (cancer, tuberculosis) by CXR as large opacities. Overall, the study showed good agreement (Somer's d = 0.64) between the predicted probabilities and observed responses of a profusion category > or = 0/1 for pathologic CWP lesions. However, the study also showed that CXR were insensitive for detecting minimal CWP lesions, and were unreliable indicators in the presence of concomitant pulmonary pathology.

Chronic occupational respiratory disease.

The authors discuss various methodologic issues pertinent to the epidemiologic study of chronic occupational lung disease. Examples to illustrate problems inherent in chronic occupational lung disease epidemiology and approaches to surmounting them are presented from the extensive literature on coal miners' lung diseases.

Coal mine dust exposure and spirometry in experienced miners.

In a previous study of new miners from the National Study of Coal Workers' Pneumoconiosis (NSCWP), researchers examined changes in spirometry values associated with coal mine dust exposure (Br J Ind Med 1993; 50:929-937). An unusual pattern of dust-related effects was observed: initial sharp decrements in FVC and FEV1 were followed by partial recovery. In the current study, similar methods were used to analyze data from experienced miners. Each of 1,915 male subjects contributed data from two of the NSCWP field surveys: either Round 1 (1969-71) and Round 2 (1972-75) and Round 4 (1985-88). From the cross-sectional analysis at Round 1 or Round 2 (R1/R2), changes of +0.6 ml FVC and -0.5 ml FEV1 were associated with each mg/m3-yr of cumulative coal mine dust exposure, but were not statistically significant (p > 0.05). From the analysis of longitudinal change in spirometry from R1/R2 to Round 4 (R4), annual declines in FVC (-0.10 ml/yr per mg/m3-yr, p = 0.003) and FEV1 (-0.07 ml/yr per mg/m3-yr, p = 0.006) were associated with pre-R1/R2 exposure. Both the pattern and the magnitude of the exposure-response relationship were different for experienced versus new miners. Possible reasons for these contrasts include differences in cumulative exposure between the two groups and the healthy worker effect among experienced miners.

Exposure-response analysis of mortality among coal miners in the United States.

The quantitative relationship between exposure to respirable coal mine dust and mortality from nonmalignant respiratory diseases was investigated in a study of 8,878 working male coal miners who were medically examined from 1969 to 1971 and followed to 1979. Exposure-related mortality was evaluated using Cox proportional hazards modeling for underlying or contributing causes of death and modified lifetable methods for underlying causes. For pneumoconiosis mortality, the lifetable analyses showed increasing standardized mortality ratios (SMRs) with increasing cumulative exposure category. Significant exposure-response relationships for mortality from pneumoconiosis (p < 0.001) and from chronic bronchitis or emphysema (p < 0.05) were observed in the proportional hazards models after controlling for age and smoking. No exposure-related increases in lung cancer or stomach cancer were observed. Pneumoconiosis mortality was found to vary significantly by the rank of coal dust to which miners were exposed. Miners exposed at or below the current U.S. coal dust standard of 2 mg/m3 over a working lifetime, based on these analyses, have an elevated risk of dying from pneumoconiosis or from chronic bronchitis or emphysema.