LIBBY, MONTANA
MINE WORKERS
Authorities analyze their mesothelioma deaths

Analysis of mesothelioma deaths in Libby mine workers.

Of the 15 mesothelioma deaths (1979–2001) identified by reviewing death certificates, 1 worker died from peritoneal mesothelioma, and 14 died from pleural (or unspecified) mesothelioma.

The SMR for mesothelioma, based on the 2 deaths that occurred in 1999–2001, was 15.1 (95% CI, 1.8–54.4). Excess mortality was also observed for several conditions to which ICD coding rubrics assigned mesothelioma deaths before 1999. For example, there was a significant excess in mortality from cancer of the pleura (SMR = 23.3; 95% CI, 6.3–59.5) and in the LTAS minor category described as "malignancy of other and unspecified sites" (SMR = 2.4; 95% CI, 1.6–3.6).

Similarly, there were 4 deaths from connective tissue cancer between 1940 and 2001, resulting in a statistically significant SMR of 4.7 (95% CI, 1.3–12.0; no lag). Lagged estimators for connective tissue cancer are not presented because small numbers likely result in unstable estimators.

Libby workers experienced significant excess mortality from asbestosis and other nonmalignant respiratory diseases. After allowing for a 15-year exposure lag, the asbestosis SMR was 165.8 (95% CI, 103.9–251.1). Mortality ratios were elevated for chronic obstructive pulmonary disease (SMR = 2.2; 95% CI, 1.7–2.9) and the LTAS minor category described as "other respiratory diseases" (SMR = 2.7; 95% CI, 1.6–4.2).

Although this report is focused on occupational respiratory disease, an a priori goal of this study was to evaluate the cohort’s mortality from other potentially asbestos-related conditions, such as circulatory disease and digestive cancer. Libby workers experienced no overall excess in heart disease (SMR = 0.9; 95% CI, 0.8–1.1), but they did experience excess mortality from circulatory diseases involving the arteries, veins, and lymphatic vessels (SMR = 1.8; 95% CI, 1.2–2.6; 29 observed vs. 16 expected; ICD-9 codes 415–417, 440–459).

Although not statistically significant, Libby workers employed for = 1 year experienced excess mortality from cancer of the liver, gallbladder, or bile ducts (SMR = 1.6; 95% CI, 0.3–4.6; 3 observed vs. 1.89 expected; ICD-9 codes 155–156), and pancreatic cancer (SMR = 1.8; 95% CI, 0.7–3.8; 7 observed vs. 3.83 expected; ICD-9 code 157).

Courtesy of National Institute of Health