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    Mortality studies

    O4.1 SILICA DUST EXPOSURE AND NON-MALIGNANT RESPIRATORY DISEASE MORTALITY AMONG SILICOTIC WORKERS IN HONG KONG: EXPOSURE-RESPONSE ANALYSES

    L. A. Tse, I. T. S. Yu.Department of Community and Family Medicine, The Chinese University of Hong Kong, HKSAR, PRC

    Introduction: Exposure-response relations between silica dust exposure and mortality from non-malignant respiratory diseases (NMRD) have been reported in other places using duration of employment, levels of silica dust exposure, and cumulative exposure as exposure indices. The aim of this study is to examine the exposure-response relations between various indices of silica dust exposure and the mortality of NMRD among a cohort of 2789 silicotic workers in Hong Kong.

    Methods: A simple job exposure matrix was developed for each industry and job task according to the documented concentrations of free respirable silica dust in Hong Kong. The geometric mean in local dusty jobs varied widely from 0.01 to 4.23 mg/m3, being highest among pneumatic drillers in underground caissons. The changes of exposure intensity with calendar year were not considered because of limited hygiene data. Exposure indices included duration of silica dust exposure, cumulative dust exposure (CDE), mean dust exposure (MDE), and radiological severity of silicosis. Cox’s proportional hazard models were fitted to examine possible exposure-response patterns, using quartiles of CDE and MDE, and log linear, log square root, log quadratic, and power models, with adjustment for age at entry into cohort, smoking pack years, history of tuberculosis, and calendar year of first exposure. The changes of –2 ln likelihood were used to compare model fit between models. The standardised mortality ratio (SMR) was calculated using the Hong Kong general population rates as reference, with indirect adjustment for smoking using Axelson’s method, in two occupational subgroups.

    Results: 371 of the 853 deaths (43.5%) occurring during 1981–99 were from NMRD other than pneumonia and other infection diseases, giving an SMR of 8.48 (95% CI 7.64 to 9.39) and a smoking …

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