Exposure to secondhand smoke from neighbours and respiratory symptoms in never-smoking adolescents in Hong Kong: a cross-sectional study

Objectives: To investigate secondhand smoke (SHS) exposure at home from neighbours in Hong Kong adolescents and its association with respiratory symptoms in never-smokers. Design: A cross-sectional study. Setting: 79 randomly selected secondary schools in Hong Kong. Participants: 61 810 secondary 1 (USA grade 7) to 7 students, in which 50 762 never-smokers were identified and included in the analysis of the association between SHS exposure at home from neighbours and respiratory symptoms. Main outcome measures: Smoking status, family smoking status, SHS exposure at home from inside the home and from neighbours in the past 7 days, respiratory symptoms and sociodemographic characteristics were reported. Adjusted ORs (AORs) of respiratory symptoms for SHS exposure from the 2 sources in never-smokers were calculated using logistic regression. Results: In all students, 33.2% were exposed to SHS at home, including 16.2% from inside the home only, 10.0% from neighbours only and 7.0% from both. The prevalence of SHS exposure from neighbours was 17.1%, including 13.5% for 1-4 days/week and 3.6% for 5-7 days/week. In never-smokers (n=50 762), respiratory symptoms were significantly associated with SHS exposure from neighbours with AORs (95% CI) of 1.29 (1.20 to 1.39) for any exposure (p<0.001), 1.21 (1.12 to 1.31) for 1-4 days/week (p<0.001) and 1.63 (1.44 to 1.86) for 5-7 days/week (p<0.001) (P for trend <0.001). Compared with no SHS exposure at home from any source, the AORs were 1.16 (1.07 to 1.25) for SHS from inside the home only (p<0.001), 1.20 (1.11 to 1.31) from neighbours only (p<0.001), and 1.74 (1.56 to 1.94) from both (p<0.001). Conclusions: SHS exposure at home from neighbours was prevalent in Hong Kong adolescents, and was associated with respiratory symptoms in never-smokers. SHS exposure at home may be underestimated by ignoring the neighbouring source. Smoke-free housing policy is needed to protect children and adolescents from harms of SHS.