Coal Workers' Pneumoconiosis–Attributable Years of Potential Life Lost to Life Expectancy and Potential Life Lost Before age 65 Years — United States, 1999–2016

Jacek M. Mazurek, MD, PhD; John Wood, MS; David J. Blackley, DrPH; David N. Weissman, MD

Disclosures

Morbidity and Mortality Weekly Report. 2018;67(30):819-824. 

Abstract and Introduction

Introduction

Coal workers' pneumoconiosis (CWP) is a preventable occupational lung disease caused by inhaling coal mine dust that can lead to premature* death.[1,2] To assess trends in premature mortality attributed to CWP,[3] CDC analyzed underlying causes of death data from 1999 to 2016, the most recent years for which complete data are available. Years of potential life lost to life expectancy (YPLL) and years of potential life lost before age 65 years (YPLL65)§ were calculated.[4] During 1999–2016, a total of 38,358 YPLL (mean per decedent = 8.8 years) and 2,707 YPLL65 (mean per decedent = 7.3 years) were attributed to CWP. The CWP-attributable YPLL decreased from 3,300 in 1999 to 1,813 in 2007 (p<0.05). No significant change in YPLL occurred after 2007. During 1996–2016, however, the mean YPLL per decedent significantly increased from 8.1 to 12.6 per decedent (p<0.001). Overall, CWP-attributable YPLL65 did not change. The mean YPLL65 per decedent decreased from 6.5 in 1999 to 4.3 in 2002 (p<0.05), sharply increased to 8.9 in 2005, and then gradually decreased to 6.5 in 2016 (p<0.001). Increases in YPLL per decedent during 1999–2016 indicate that over time decedents aged ≥25 years with CWP lost more years of life relative to their life expectancies, suggesting increased CWP severity and rapid disease progression. This finding underscores the need for strengthening proven prevention measures to prevent premature CWP-associated mortality.

The National Vital Statistics System's multiple cause-of-death data during 1999–2016 were analyzed to examine CWP mortality. For this analysis, CWP deaths were identified from death certificates listing the International Classification of Diseases, Tenth Revision (ICD-10) code J60 (coal workers' pneumoconiosis) as the underlying cause of death. Because CWP is entirely attributable to occupational exposure,[1] only deaths of persons aged ≥25 years were considered. Years of potential life lost to life expectancy (YPLL) and before age 65 years (YPLL65) were calculated for each decedent. Time-trends in death rates (per 1 million population), age-adjusted to the 2000 U.S. standard population and YPLL/YPLL65, were assessed.[5] Information on decedents' usual industry and occupation** was coded†† in accordance with the U.S. Census 2000 Industry and Occupation Classification System.

During 1999–2016, 4,344 decedents aged ≥25 years had CWP assigned as the underlying cause of death, accounting for 38,358 YPLL (mean per decedent = 8.8). Among these decedents, 369 (8.5%) were aged 25–64 years, accounting for 2,707 YPLL65 (mean per decedent = 7.3) (Table). Overall, CWP deaths among U.S. residents aged ≥25 years significantly decreased (73%), from 409 in 1999 to 112 in 2016 (Table) (Figure 1). The decline was steeper during 1999–2008 (p<0.01) than during 2008–2016 (p<0.001). CWP deaths among U.S. residents aged ≥65 years decreased 77%, from 389 in 1999 to 88 in 2016. The decline was steeper during 1999–2008 (p<0.001) than during 2008–2016 (p<0.001). Among U.S. residents aged 25–64 years, there was no significant change in the number of CWP deaths during 1999–2016 (Table).

Figure 1.

Age-adjusted coal workers' pneumoconiosis deaths and deaths* per million persons aged ≥25 years with coal workers' pneumoconiosis, by year of death — United States, 1999–2016
Source: National Vital Statistics System. https://wonder.cdc.gov.
*Adjusted to the 2000 U.S. standard population.
Decedents whose death certificates listed the International Classification of Diseases, Tenth Revision (ICD-10) code J60 (coal workers' pneumoconiosis) as the underlying cause of death.

Age-adjusted CWP death rates among U.S. residents aged ≥25 years declined 81%, from 2.31 per million in 1999 to 0.44 in 2016 (annual percent change [APC] = −9.0%; 95% confidence interval [CI] = −9.6 to −8.3; p<0.05) (Figure 1). Age-adjusted CWP death rates among residents aged ≥65 years declined 84% from 11.30 per million in 1999 to 1.82 in 2016 (APC = −9.6%; 95% CI = −10.3 to −8.9; p<0.05).

The CWP-attributable YPLL decreased 42.8% from 3,300 in 1999 to 1,413 in 2016 (Table) (Figure 2). The decline was steeper during 1999–2007 (p<0.001) than during 2007–2016 (p<0.05). During 1999–2016, the mean YPLL per decedent increased 55.6%, from 8.1 to 12.6 years per decedent. No significant change in the mean YPLL per decedent was observed during 1999–2003; however, mean YPLL per decedent increased significantly from 2003 to 2016 (p<0.001).

Figure 2.

Years of potential life lost to life expectancy (YPLL) and before age 65 years (YPLL65) and mean YPLL and YPLL65 per decedent for decedents aged ≥25 years with coal workers' pneumoconiosis,* by year of death — United States, 1999–2016
Source: Multiple cause-of-death data, National Center for Health Statistics, CDC.
*Decedents whose death certificates listed the International Classification of Diseases, Tenth Revision (ICD-10) code J60 (coal workers' pneumoconiosis) as the underlying cause of death.

CWP-attributable YPLL65 varied annually, from a high of 271 (mean per decedent = 8.5) in 2009 to a low of 65 (mean per decedent = 5.4) in 2001 (Table) (Figure 2). Overall, no change in the YPLL65 from 1999 to 2016 was observed. The time-trend analysis indicates that the mean CWP-attributable YPLL65 per decedent aged 25–64 years decreased 34% from 6.5 YPLL65 per decedent in 1999 to 4.3 in 2002 (p<0.05), sharply increased 107% to 8.9 in 2005 (p = 0.06), and then gradually decreased 27% to 6.5 in 2016 (p<0.001). In these three respective periods, highest mean YPLLs65 per decedent were 7.2 in 2000; 9.6 in 2004, and 9.3 in 2008.

During 1999–2016, ≥10 CWP deaths among persons aged ≥25 years occurred in 27 states. Deaths in Pennsylvania (1,360; 9,109 YPLL; mean per decedent = 6.7), West Virginia (892; 8,543 YPLL; 9.6), Virginia (558; 6,013 YPLL; 10.8), and Kentucky (554; 6,422 YPLL; 11.6) accounted for 77.6% of all decedents and 78.4% of the total YPLL (Table). CWP deaths among persons aged 25–64 years in Kentucky (95; 650 YPLL65; mean per decedent = 6.8), West Virginia (86; 507 YPLL65; 5.9), Virginia (84; 649 YPLL65; 7.7), and Pennsylvania (24; 172 YPLL65; 7.2), accounted for 78.3% of all decedents and 73.1% of the total YPLL65.

Industry and occupation data were available for 740§§ (94.6%) of 782 CWP deaths among U.S. residents aged ≥25 years that occurred in 26 states during 1999, 2003, 2004, and 2007–2012 (Table). By industry, three quarters of deaths occurred among residents who worked in the coal mining industry (560; 75.7%) accounting for 5,415 YPLL (mean per decedent = 9.7). By occupation, approximately two thirds of deaths occurred among mining machine operators (504; 68.1%) accounting for 4,822 YPLL (mean per decedent = 9.6). Remaining CWP deaths were associated with 68 other industries and 79 other occupations.

*Early pneumoconiosis (i.e., simple CWP) is often asymptomatic, but the disease can progress to more severe forms associated with substantial impairment, including progressive massive fibrosis. Progression can occur despite cessation of exposure. Progression might be more rapid after high levels of exposure to coal mine dust or if the dust has a high respirable crystalline silica content. There are no accepted specific therapies to prevent progression of CWP.
Underlying cause of death is defined as "the disease or injury which initiated the chain of morbid events leading directly to death, or the circumstances of the accident or violence which produced the fatal injury." https://webappa.cdc.gov/ords/norms.html.
§YPLL to life expectancy may be considered as a loss of years from the overall life span. YPLL to life expectancy was a sum of the differences between the age at death and life expectancy for each decedent, internally adjusted by race and sex (https://www.cdc.gov/nchs/products/life_tables.htm). YPLL65 may be considered as a loss of years from a traditional working life. YPLL65 were calculated as a sum of the differences between age 65 years and the age at death for each decedent.
The Joinpoint Regression program fits the simplest joinpoint model that the data allow. It determines years when changes in the number of deaths/YPLL/mean YPLL per decedent and the annual percentage change in log-transformed age-adjusted mortality rate occur by performing a sequence of permutation tests using Monte Carlo sampling and the Bonferroni correction for multiple testing. The overall statistical significance level was α = 0.05, with a maximum of three joinpoints and four trend segments allowed.
**Twenty-six states provided data for the years 1999, 2003, 2004, and 2007–2012: Colorado, Florida, Georgia, Hawaii, Idaho, Indiana, Kansas, Kentucky, Louisiana, Michigan, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, North Carolina, North Dakota, Ohio, Rhode Island, South Carolina, Texas, Utah, Vermont, Washington, West Virginia, and Wisconsin. The state represents the state where the death took place. https://www.cdc.gov/niosh/topics/noms/default.html.
†† https://webappa.cdc.gov/ords/norms-glossary.html#ind-occ.
§§For 42 residents of these 26 states, deaths occurred in states other than the state of residence that did not code the industry and occupation information.

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