Frequency–risk relationships between second-hand smoke exposure and respiratory symptoms among adolescents: a cross-sectional study in South China

OBJECTIVES: Although previous studies have suggested an association between second-hand smoke (SHS) exposure and respiratory symptoms, current evidence is inconsistent. Additionally, it remains unclear whether there are frequency–risk relationships between SHS exposure and respiratory symptoms among adolescents. METHODS: A cross-sectional survey was conducted using a stratified cluster sampling method to obtain a representative sample of high school students in Guangzhou, China. The respiratory symptoms were defined as persistent cough or sputum for three consecutive months during the past 12 months. Self-reported SHS exposure was defined as non-smokers' inhalation of the smoke exhaled from smokers on ≥1 day a week in the past 7 days. The univariable and multivariable logistic regression models were fitted to explore the potential frequency–risk relationships between SHS exposure and respiratory symptoms. RESULTS: Among 3575 students, the overall prevalence of SHS exposure was 69.2%, including 49.5% for SHS in public places, 34.5% in homes, 22.7% in indoor campuses and 29.2% in outdoor campuses. There were significantly increased risks of having respiratory symptoms corresponding to SHS exposure in public places (OR=1.60, 95% CI 1.30 to 1.95), in homes (OR=1.53, 95% CI 1.25 to 1.87), in indoor campuses (OR=1.43, 95% CI 1.14 to 1.79) and in outdoor campuses (OR=1.37, 95% CI 1.10 to 1.69) using no exposure as reference. Notably, we observed monotonic frequency–risk relationships between setting-specific(eg, homes, public places and campuses) SHS exposure and respiratory symptoms. CONCLUSION: Our findings suggest that setting-specific SHS exposure is associated with a significant, dose-dependent increase in risk of respiratory symptoms.