Cross-Sectional and Prospective Associations Between Passive Smoking and Respiratory Symptoms at the Workplace

Purpose: The purpose of the study is to investigate the cross-sectional and prospective relation between workplace secondhand smoke (SHS) exposure and respiratory symptoms. Methods: Cross-sectional data for workplace SHS exposure and respiratory symptoms were collected by using random digit dialing from 7336 never-smoking Hong Kong workers 15 years or older in 1997 to 1998. In the 2000 to 2001 follow-up, 2213 workers who remained never smoking, had the same SHS exposure status, worked at the same job for at least 2 years, and were not exposed to SHS at home at follow-up were included for prospective analysis. Results: Cross-sectionally, SHS was associated significantly with frequent colds, cough and phlegm, throat problems, and the presence of any respiratory symptoms with adjusted odds ratios of 1.89 (95% confidence interval [CI], 1.66-2.15), 1.65 (95% CI, 1.35-2.02), 1.88 (95% CI, 1.63-2.15), and 1.96 (95% CI, 1.75-2.20) at baseline, each having significant linear associations with duration of exposure. SHS was not associated with rhinitis. Prospectively, consistent SHS exposure increased the risk for cough and phlegm and any respiratory symptoms by 48% (12% to 97%) and 54% (13% to 109%), respectively. Conclusions: This first non-Western population-based prospective study shows that workplace SHS exposure is associated significantly with frequent respiratory symptoms, both cross-sectionally and prospectively, thus providing strong evidence that the association is causal.