Respiratory cancer and other chronic disease mortality among silicotics in California

Silicotics have increased mortality from tuberculosis (TB) and from nonmalignant respiratory diseases (NMRD), including silicosis and silicotuberculosis. Since the publication of the International Agency for Research on Cancer monograph in 1987 indicating that silica was a probable human carcinogen, there has been an extensive debate about the cancer risks among silicotics. The authors identified 590 claims for silicosis among a registry of lung diseases compiled from California Workers' Compensation cases from 1945 to 1975. Using state vital records, we determined the mortality risks from 1946 to 1991. Our findings confirmed that these claimants had a significantly elevated risk for all causes of death with a standardized mortality ratio (SMR) of 1.30 (95% confidence interval [CI] = 1.18, 1.43); TB had a SMR of 56.35 (95% CI = 41.10, 75.40) and NMRD a SMR of 3.80 (95% CI = 3.11, 4.60). Cancers of the trachea, bronchus, and lung had a SMR of 1.90 (95% CI = 1.35, 2.60). For malignancies of the large intestine, there was a previously unreported SMR of 2.08 (95% CI = 1.14, 3.50). Mortality from all diseases of the heart was significantly less than expected with a SMR of 0.68 (95% CI = 0.55, 0.83); cancers of the prostate and lymphatic system were also significantly low with SMRs of 0.26 (95% CI = 0.03, 0.94) and 0.17 (95% CI = 0.04, 0.97), respectively. Workers with silicosis should be warned about these chronic disease risks, and prevention efforts to control occupational silica dust exposure should become a higher priority.