title: Joint effects of smoking and silicosis on diseases to the lungs.
abstract: Smokers are subject to being more susceptible to the long-term effects of silica dust, whilst it remains unclear whether the joint effect of smoking and silicosis differs amongst diseases to the lungs; this study aims to address this knowledge gap. This was a historical cohort study comprised of 3202 silicotics in Hong Kong during 1981-2005 who were followed up till 31/12/2006. We estimated the standardized mortality ratio (SMR) in the smoking and never smoking silicotics using the mortality rates of male general population indiscriminately by smoking status, but these SMRs were regarded as biased. We adjusted these biased SMRs using "smoking adjustment factors (SAF)". We assessed the multiplicative interaction between smoking and silicosis using 'relative silicosis effect (RSE)' that was the ratio of SAF-corrected SMR of smoking silicotics to the never smokers. A RSE differs significantly from one implies the presence of multiplicative interaction. A significant excess SMR was observed for respiratory diseases (lung cancer, chronic obstructive pulmonary diseases [COPD], silicosis) and other diseases to the lungs (pulmonary heart disease, tuberculosis). All the 'biased-SMRs' in smokers were higher than those in never smokers, but the SAF-corrected SMRs became higher in never smokers. The RSE was 0.95 (95%CI: 0.37-3.55), 0.94 (95%CI: 0.42-2.60), and 0.81 (95%CI: 0.60-1.19) for lung cancer, COPD, and silicosis; whilst it was 1.21 (95%CI: 0.32-10.26) for tuberculosis and 1.02 (95%CI: 0.16-42.90) for pulmonary heart disease. This study firstly demonstrated the joint effect of smoking and silicosis may differ amongst diseases to the lungs, but power is limited.
authors.affiliation: JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong SAR, China.
authors.forename: Lap Ah
authors.initials: LA
authors.lastname: Tse
authors.affiliation: JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong SAR, China.
authors.forename: Ignatius T S
authors.initials: IT
authors.lastname: Yu
authors.affiliation: JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong SAR, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Qiu
authors.affiliation: Pneumoconiosis Clinic, Tuberculosis and Chest Service, Department of Health, Hong Kong SAR, China.
authors.forename: Chi Chiu
authors.initials: CC
authors.lastname: Leung
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015331:Cohort Studies; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008168:Lung / Q000473:pathology; D008171:Lung Diseases / Q000150:complications / Q000453:epidemiology / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D012829:Silicosis / Q000150:complications / Q000453:epidemiology / Q000401:mortality*; D012907:Smoking / Q000009:adverse effects*; D055815:Young Adult
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