Involuntary tobacco smoke exposure from multiple sources and respiratory symptoms in Hong Kong adolescents

Abstract

Most studies on the harms of involuntary tobacco smoke exposure in adolescents focus solely on secondhand smoke (SHS) from smoking inside the home. Other sources, such as SHS exposure outside home, are seldom considered. Recent studies have addressed that SHS drifting into the home from outside and thirdhand smoke (THS), the residual cigarette smoke, are also potential sources. The prevalence and associated health outcomes of these 2 emerging sources of tobacco smoke in adolescents have not yet been reported. Therefore, I investigated involuntary tobacco smoke exposure from multiple sources, separately and collectively, in Hong Kong adolescents, including the prevalence and associations with respiratory symptoms.

The Smoking and Health Survey among Hong Kong Secondary School Students 2010/11, an anonymous survey, was conducted in 62083 students from 79 randomly selected schools. Students reported their exposure to 4 sources of tobacco smoke, namely SHS at home from inside the home, SHS at home from neighbours, SHS outside home and THS at home. They also reported their smoking status, respiratory symptoms and other information. After excluding questionnaires with poor quality, 61810 students (mean age 14.7±2.0, 50.8% boys) remained for analyses. Prevalence of exposure to the 4 sources of tobacco smoke in all students were calculated and weighted by age, sex and grade. Associations of the exposure with respiratory symptoms were analysed in never smokers using logistic regression.

Overall, 63.3% of adolescents reported tobacco smoke exposure, including 23.2% to SHS from inside the home, 17.1% to SHS from neighbours, 55.3% to SHS outside home and 16.9% to THS at home. One-third (33.2%) were exposed to SHS at home from any source. The prevalence would be underestimated by 30.1% if SHS from neighbours was ignored. In both smoking and non-smoking families, adolescents exposed to SHS had higher odds of THS exposure at home than the unexposed.

Never smokers exposed to any tobacco smoke from the 4 sources had 15% higher odds of respiratory symptoms than the unexposed. For each source, exposure for more days per week was associated with higher odds of respiratory symptoms, compared with no exposure to the corresponding source. The adjusted odds ratios of respiratory symptoms were 1.21 (1.13-1.30) for any SHS at home from inside the home, 1.28 (1.19-1.38) for any SHS at home from neighbours, 1.04 (0.98-1.11) for any SHS outside home and 1.22 (1.12-1.34) for any THS at home. Doseresponse association was also observed between the number of sources of tobacco smoke exposure and respiratory symptoms. The odds of respiratory symptoms was 4% higher for exposure to any 1 source, 12% higher for any 2, 40% higher for any 3 and 99% higher for 4.

In conclusion, notwithstanding the low smoking prevalence in Hong Kong, involuntary tobacco smoke exposure in adolescents was common. Tobacco smoke exposure from different sources were respectively associated with respiratory symptoms in dose-response fashion in never smokers. Exposure to more sources was associated with higher odds of respiratory symptoms. The findings warrant more aggressive tobacco control policies to protect adolescents from involuntary tobacco smoke exposure.