Pneumoconiosis and Advanced Occupational Lung Disease Among Surface Coal Miners — 16 States, 2010–2011

Coal workers' pneumoconiosis (CWP) is a chronic occupational lung disease caused by long-term inhalation of dust, which triggers inflammation of the alveoli, eventually resulting in irreversible lung damage. CWP ranges in severity from simple to advanced; the most severe form is progressive massive fibrosis (PMF). Advanced CWP is debilitating and often fatal. To prevent CWP, the Coal Mine Health and Safety Act of 1969 established the current federal exposure limit for respirable dust in underground and surface coal mines. The Act also established a surveillance system for assessing prevalence of pneumoconiosis among underground coal miners, but this surveillance does not extend to surface coal miners. With enforcement of the exposure limit, the prevalence of CWP among underground coal miners declined from 11.2% during 1970–1974 to 2.0% during 1995–1999, before increasing unexpectedly in the last decade, particularly in Central Appalachia (1,2). Exposure to respirable dust is thought to be less in surface than underground coal miners. Although they comprise 48% of the coal mining workforce, surface coal miners have not been studied since 2002 (3,4). To assess the prevalence, severity, and geographic distribution of pneumoconiosis among current surface coal miners, CDC obtained chest radiographs of 2,328 miners during 2010–2011 through the Coal Workers' Health Surveillance Program of the National Institute for Occupational Safety and Health (NIOSH). Forty-six (2.0%) of 2,257 miners with >1 year of surface mining experience had CWP, including 37 who had never worked underground. Twelve (0.5%) had PMF, including nine who had never worked underground. A high proportion of the radiographs suggested silicosis, a disease caused by inhalation of crystalline silica. Surface coal mine operators should monitor worker exposures closely to ensure that both respirable dust and silica are below recommended levels to prevent CWP. Clinicians should be aware of the risk for advanced pneumoconiosis among surface coal miners, in addition to underground coal miners, to facilitate prompt disease identification and intervention.

During 2010–2011, the Coal Workers' Health Surveillance Program mobile surveillance unit traveled to 16 of the 17 states* with active surface coal mines to offer chest radiographs to miners. Site selection was based on accessibility and cooperation of surface coal mine operators, who are not required to offer chest radiographs to their employees. All participants provided written informed consent.

Work histories, including tenures in surface and underground coal mining, were collected from each miner. Radiographs were classified for changes consistent with CWP, according to the International Labour Office (ILO) International Classification of Radiographs of Pneumoconiosis (5). At least two NIOSH B Readers† who had no knowledge of miners' work history, performed the classifications (5). Identification of CWP required agreement between two readers that small pneumoconiotic opacities were present at an ILO profusion subcategory of ≥1/0 (range: 0/0–3/+). An ILO profusion subcategory of ≥2/1 was considered advanced pneumoconiosis. Identification of PMF required reader agreement on the presence of large (>1 cm) pneumoconiotic opacities (A, B, or C) (5). B Readers also recorded the presence of r-type radiographic opacities (rounded opacities, 4–10mm in diameter), which have been associated with inhalation of crystalline silica, a common exposure in mining (6). If the classifications of the presence or severity of pneumoconiosis by two B Readers were not in agreement, the radiograph was sent for classification to a third B Reader.

The crude prevalences of CWP, PMF, advanced pneumoconiosis, and r-type opacities among participating surface coal miners were calculated. Prevalences of diseases among miners from the three Central Appalachian states (Kentucky, Virginia, and West Virginia) were compared with prevalences among miners from the 13 other mining states; prevalence ratios were calculated using log binomial regression, adjusting for important confounders.

Radiographs from 2,328 surface coal miners (approximately 7% of active U.S. surface coal miners) were evaluated and classified. Among participants, 95% were men, and 83% were non-Hispanic whites. Of 2,257 (97%) miners who reported ≥1 year of surface mining tenure, 46 (2.0%) had CWP (Table), including 37 who reported no underground mining experience; 12 (0.5%) had CWP that had progressed to PMF (Table), including nine who had never worked underground. Among the 46 miners with CWP, 17 (37%) were classified as having advanced pneumoconiosis (≥2/1 ILO profusion category), and 17 (37%) were found to have r-type opacities (Table) (6).

Of the participating surface coal miners, 833 were from Central Appalachia, and 1,424 were from the other 13 states. Crude prevalences of CWP (31 miners [3.7%]) and PMF (10 [1.2%]) were higher among the Central Appalachian miners than the non–Central Appalachian miners (15 [1.1%] and two [0.1%], respectively) (Table). In addition, crude prevalences of advanced pneumoconiosis and r-type opacities were higher among the Central Appalachian miners (11 [1.3%] and 14 [1.7%], respectively) than the miners from the other 13 states (six [0.4%] and seven [0.5%], respectively)

The median total mining tenure differed significantly between Central Appalachian (28 years) and other surface miners (20 years) (Table). Adjustment for tenure was performed because the development and severity of CWP is directly related to both duration and concentration of dust exposure. After adjustment, results from a log-binomial regression among 2,102 miners for whom surface mining comprised ≥75% of their total mining tenure indicated that the prevalence of CWP was 2.7 times greater (95% confidence interval = 1.4–5.3) among Central Appalachian miners compared with the other miners (Figure). Tenure-adjusted prevalences of both PMF and r-type opacities also were significantly higher in Central Appalachian miners (Figure).

Reported by

A. Scott Laney, PhD, Anita L. Wolfe, Edward L. Petsonk, MD, Div of Respiratory Disease Studies, National Institute for Occupational Safety and Health; Cara N. Halldin, PhD, EIS Officer, CDC. Corresponding contributor: Cara N. Halldin, [email protected], 304-285-5899.

Editorial Note

This analysis indicates that some currently working surface coal miners with little or no underground mining experience suffer from severe preventable respiratory disease, even though surface miners are thought to work in conditions less dusty than the confined work spaces of underground miners. The specific appearance of the abnormalities (r-type opacities) observed on the miners' chest radiographs suggests that inhalation of respirable crystalline silica might be a key exposure. Dusts containing >5% respirable crystalline silica are more fibrogenic, and inhalation can lead to accelerated onset and greater severity of lung disease (7,8).

Surface coal miners in Central Appalachia had greater prevalence of both CWP and PMF compared with miners in other regions, independent of mining tenure, age, or underground working experience. Causes for these regional differences are unknown but might reflect differences in mining practices, safety culture, or geology. These findings suggest that current federal permissible dust exposure limits might be insufficient to protect against disease or are not being adequately controlled to prevent excess dust exposure.

The findings in this report are subject to at least three limitations. First, this study used a sample based on accessibility and cooperation of mine operators and voluntary participation of miners. Whether any selection factors affected miner participation is unclear; therefore, prevalence of CWP might not be representative of all U.S. surface coal miners. Prevalence of CWP might be overestimated or underestimated, depending on whether miners with symptoms were more or less likely to volunteer for chest radiography. Second, age and mining tenure were self-reported, which could affect comparisons of tenure-adjusted disease prevalence. Finally, estimates of the prevalence of CWP and PMF included assessment of miners with underground mining experience, 155 (6.9%) of whom had ≥25% of their total mining tenure in underground mines. Therefore, morbidity in these surface miners cannot be attributed to their work as surface miners alone.

Surface coal miners and the clinicians caring for them should be aware of the risk for CWP and PMF, medical conditions traditionally associated with underground coal mining. Surface coal mine operators should inform workers of their risk for advanced pneumoconiosis and closely monitor exposures, ensuring that respirable dust and silica exposures are continuously below recommended levels to reduce the risk for pneumoconiosis.

To prevent pneumoconiosis among underground and surface coal miners, the Coal Mine Health and Safety Act established federal exposure limits for respirable silica and coal dust.§ NIOSH has recommended changes to the manner in which respirable silica and coal dust are measured for compliance and enforcement purposes (9,10). Use of personal continuous dust monitoring devices is recommended to achieve a more accurate and representative assessment of workers' exposure, although these devices currently cannot distinguish between silica and coal dust (10). The NIOSH-recommended exposure limit for respirable silica is 50 µg/m3, as a time-weighted average¶ (8). Additionally, NIOSH recommends that surface coal miners be included in periodic health surveillance that is similar to that conducted for underground miners (9,10).

Acknowledgments

Members of the Coal Workers' Health Surveillance Program mobile surveillance team and surface coal miner participants. Kristin J. Cummings, MD, Div of Respiratory Disease Studies, National Institute for Occupational Safety and Health; Derek Ehrhardt, MPH, Unice Oleander, Global Immunization Div, Center for Global Health, CDC.

References

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