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Advanced Cases of Coal Workers' Pneumoconiosis --- Two Counties, Virginia, 2006
This report describes 11 newly identified cases of advanced coal workers' pneumoconiosis (CWP), including progressive massive fibrosis (PMF), in working coal miners from Lee and Wise counties in southwestern Virginia. PMF is a disabling and potentially fatal form of CWP, an occupational lung disease caused by the inhalation of coal mine dust. The continuing occurrence of advanced forms of CWP emphasizes the importance of comprehensive measures to control coal mine dust effectively and reduce the potential for inhalation exposures in coal mining.
The Federal Coal Mine Health and Safety Act of 1969 mandated dust limits in the mining environment to protect the respiratory health of coal miners (1) and created a health surveillance program for underground miners subsequently administered by the National Institute for Occupational Safety and Health (NIOSH). After dust levels were lowered, data from the surveillance program documented reductions in the prevalence of CWP among active coal miners (2). Nonetheless, during 1996--2002, clusters of rapidly progressive CWP were identified among miners in certain areas of the United States, predominantly in eastern Kentucky and western Virginia (3).
The advanced cases of CWP in southwestern Virginia described in this report were identified through the Enhanced Coal Workers' Health Surveillance Program (ECWHSP), which was initiated in March 2006 through collaboration between NIOSH and the Mine Safety and Health Administration (MSHA). ECWHSP, which uses a mobile examination unit to provide respiratory health evaluations in areas easily accessible to U.S. coal miners, aims to increase miner participation in surveillance for early detection of dust-related lung disease and to target areas for prevention. Standardized questionnaires, spirometry (lung-capacity testing), and chest radiography are administered according to NIOSH-specified procedures. Radiographs are classified by NIOSH-certified B Readers according to the International Labour Office (ILO) International Classification of Radiographs of Pneumoconioses (4).
In March and May 2006, a total of 328 (31%) of the estimated 1,055 underground coal miners currently employed in Lee and Wise counties in Virginia were examined in ECWHSP surveys. The mean age of examined miners was 47 years (range: 21--63 years), and their mean tenure working in underground coal mines was 23 years (range: 0--41 years). A total of 216 (66%) had worked at the coal face (i.e., the cutting surface where coal is sheared from the wall and dust levels typically are greatest) for >20 years. A total of 30 (9%) examined miners had radiographic evidence of pneumoconiosis (i.e., category 1/0 or higher profusion of small opacities*). Of these, 11 miners had advanced cases, including five with large opacities consistent with PMF and six with coalescence of small opacities on a background profusion of category 2.
Among the 11 miners with advanced cases, the mean age was 51 years (range: 39--62 years), the mean tenure in underground coal mines was 31 years (range: 17--43 years), and the mean number of years working at the coal face was 29 years (range: 17--33 years) (Table 1). All 11 miners with advanced cases met radiographic criteria for rapidly progressive CWP (3). All reported at least one respiratory symptom, the most common being dyspnea (shortness of breath). Of the nine who had spirometry, four had abnormal results (Table 2).
Reported by: VC Antao, MD, EL Petsonk, MD, MD Attfield, PhD, Div of Respiratory Disease Studies, National Institute for Occupational Safety and Health, CDC.
In 1969, the Federal Coal Mine Health and Safety Act established a mandatory limit on respirable dust exposure that was intended to eliminate advanced forms of pneumoconiosis among U.S. coal miners (1). Nonetheless, the findings in this report indicate that 11 miners in Lee and Wise counties, including nine (i.e., miners 3--11) who had not worked before the 1969 limit was imposed, have advanced CWP. Identification of these cases corroborated previous findings of geographic clustering of rapidly progressive disease in western Virginia (3).
Based on an epidemiologic exposure-response model developed using data from a large population of U.S. underground coal miners (5), the expected number of cases of CWP with profusion category 2 or higher can be estimated for the 328 examined miners at exposure to various levels of coal mine dust. After 1974, average dust concentrations for coal-face miners in these counties, based on measurements reported to MSHA by mine operators, was 1.2 mg/m3 (Figure). Using the age and tenure for each of the 328 examined miners and applying different levels of respirable dust exposure to high-volatile (i.e., low or medium rank) bituminous coal, the expected number of cases of category 2 or higher CWP would be 3.7 cases at 1 mg/m3 and 5.5 cases at the current permissible exposure limit of 2 mg/m3 (for coal mine dust with <5% silica content). This number of cases amounts to half the actual number of 11 advanced cases identified in this study, which is similar, as defined by the model, to the 11.9 cases that would be expected had the miners been exposed to an average dust concentration of 4 mg/m3.
Several reasons might explain the continued occurrence of advanced cases of CWP among miners. The current federal underground coal mine respirable dust limit of 2 mg/m3 might be too high. In 1995, NIOSH concluded that the current limit would not eliminate advanced disease and established a recommended exposure limit (REL) of 1 mg/m3 (6). In addition, although reported average coal mine dust levels during 1970--2005 were lower than the current 2 mg/m3 standard (Figure), and only approximately 2.5% of individual samples exceeded this value, previous studies have indicated that compliance measurements might be subject to systematic bias and underestimate actual exposures (7,8). Exposures to silica dust during coal mining also might contribute to acquiring advanced pneumoconiosis (9). Only since 2001 have mean levels of silica in coal mine dust for underground miners in Lee and Wise counties been reported as low as the NIOSH REL of 0.05 mg/m3 (Figure). During 1982--2000, approximately 65% of the silica air samples collected by MSHA inspectors in these counties exceeded the NIOSH REL. Finally, the severity of disease might have been increased in part because of the toxicity of the coal being mined. NIOSH acknowledges that the risk for disease can vary with type of coal (6); however, the types of coal found in the two Virginia counties have not been previously associated with increased toxicity.
The findings in this report are subject to at least two limitations. First, participation was limited to 31% because of the time and resource constraints of the survey staff and other factors (e.g., equipment problems and a snowstorm). Second, migration between counties and frequent job changes are common among miners. At the time of the survey, only three of the 11 miners had worked for their current mine for >5 years. However, although these factors might have led to misestimation of the actual prevalence of CWP and PMF in this region, the occurrence of advanced cases of CWP among current miners should be considered a sentinel health event and justifies a comprehensive assessment of current dust-control measures.
NIOSH will expand medical surveillance activities in southwestern Virginia and elsewhere and continue collaborations with MSHA to increase protection of coal miners. Detailed information regarding exposures, mining conditions, dust controls, and coal composition is needed to improve preventive measures. To assess the effectiveness of current prevention and enforcement strategies, NIOSH is reviewing dust-control plans and examining mining conditions (including airborne silica dust levels) in southwestern Virginia and other mining areas where rapidly progressive CWP has been identified. These activities will help NIOSH make appropriate recommendations to MSHA and other agencies and improve ongoing surveillance and intervention measures. Coal mine operators should strive to maintain the lowest possible dust levels, at least consistent with the current compliance limits for coal mine dust and silica and preferably below the NIOSH RELs.
This report was based, in part, on data collected and compiled by ECWHSP staff members.
* The ILO classification categorizes the profusion of small opacities by comparing with standard radiographs using a 12-point scale from 0/- (normal) to 3/+ (greatest), and the presence and severity of large pneumoconiotic opacities (i.e., PMF) as stages A (least severe PMF), B, or C (most severe PMF).
Data from MSHA coal mine inspector and mine operator samples.
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Date last reviewed: 8/24/2006