Cross-Sectional and Prospective Associations Between Passive Smoking and Respiratory Symptoms at the Workplace
Introduction
The effects of secondhand smoke (SHS) on such fatal chronic diseases as lung cancer and heart disease in adults are well established (1). Such diseases typically are irreversible and have a long latent period. Conversely, respiratory symptoms are much milder, reversible, and more common in both adults and children. Existing findings tend to support a positive association between SHS and respiratory symptoms in adults, but they are based mainly on cross-sectional studies. Although the California Environmental Protection Agency concluded that the association between SHS and chronic respiratory symptoms in children is causal, the evidence in adults is considered only suggestive (2). A recent comprehensive review by Jaakkola and Jaakkola (3) also showed mixed findings in 12 cross-sectional studies 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 published up to 2000. Since then, four more studies were published 16, 17, 18, 19. Of these 16 studies, eight measured SHS exposure in the home 4, 5, 6, 7, 8, 9, 11, 12, four measured SHS exposure in the workplace 10, 16, 17, 19, and four measured SHS exposure in both places 13, 14, 15, 18. Most studies were based on Western nations, and only three studies were conducted elsewhere; one in mainland China (11), one in Hong Kong (15), and one in Singapore (12).
Ten studies provided results for home SHS exposure 4, 5, 6, 7, 8, 9, 11, 12, 15, 18; seven of these were Western studies. Of different respiratory symptoms examined, only one of seven studies found a significant association in women between dyspnea and SHS exposure from husbands, with an odds ratio (OR) of 1.56 (7). However, some significant findings were observed in all three Asian studies. There were six Western studies 10, 13, 14, 17, 19, 20 and one Hong Kong study (15) of workplace SHS exposure. In another European study, Larsson et al. (18) measured SHS exposure outside the home, implying workplace as a major component. All eight studies showed significant findings. Only three prospective studies were published on the topic, all sampling Western populations with small sample sizes, and results were mixed 21, 22, 23.
Results of SHS exposure on respiratory symptoms tended to differ according to the study population and whether home or workplace exposure was measured. Western studies mostly showed no association for home exposure, but were positive for workplace exposure. Asian studies generally yielded positive results for both home and workplace exposure, but there were few studies and none were prospective. No study examined the association between SHS exposure and respiratory symptoms both cross-sectionally and prospectively.
The objective of the present prospective study is to investigate the association between workplace SHS exposure and respiratory symptoms in the general working population of Hong Kong based on both cross-sectional and prospective analyses.
Section snippets
Methods
Two occupational health telephone surveys were conducted in 1997 to 1998 and 2000 to 2001 on the same respondents in Hong Kong. The baseline survey used random digit dialing to sample households throughout the territory. Telephone numbers were selected randomly from the most recent residential telephone directories, and the last digit was replaced by a random number. This increased the likelihood that the numbers used were valid residential numbers, while allowing new or unlisted household
Results
Table 1 lists baseline characteristics of respondents for the cross-sectional and prospective analysis. They most commonly were aged between 30 and 39 years, had secondary level education, and worked as clerks, service, and shop sales. Workplace SHS exposure was reported in 35.8% and 19.7% of respondents selected for cross-sectional and prospective analyses, respectively. Criteria of selecting respondents without home exposure to SHS and with stable job positions seemed to favor those with
Discussion
To the best of our knowledge, this is the largest population-based prospective study of SHS and common respiratory symptoms and the first in non-Western populations. In cross-sectional analysis, we found positive associations between workplace SHS exposure and such respiratory symptoms as frequent cold, cough and phlegm, and throat problem, with significant linear trends for duration of exposure. Respiratory symptoms used in different studies might not be the same, but the positive associations
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Funded by the Hong Kong Occupational Safety and Health Council.