The association of respiratory symptoms with secondhand and thirdhand smoke exposure in Hong Kong primary school students

Abstract

Introduction: Exposure to secondhand smoke (SHS) causes respiratory diseases in children. However, little is known about the hazard of thirdhand smoke (THS) and secondhand smoke at home that comes from neighbourhood. This survey aims to investigate the association of respiratory symptoms with exposure to SHS at home from inside home, SHS at home from neighbourhood, THS at home, and SHS outside home in Hong Kong primary school students. The association of respiratory symptoms with different combinations of SHS and THS exposure was also investigated.

Methods: This was a cross-sectional study conducted in 2010-11 with 20015 primary 4-6 (P4-6) students from 96 randomly selected schools in Hong Kong to collect self-reported data, using a purposely-designed questionnaire, from school-aged children on relevant demographics, respiratory symptoms and exposure to SHS and THS.

To investigate the association of respiratory symptoms with SHS and THS exposure in never smoking and ever smoking primary school students, logistic regression analyses were conducted adjusting for potential confounders (age, sex, place of birth and number of bedrooms), and with mutual adjustment of various tobacco smoke exposures.

Results: In never smoking primary students, compared with the unexposed group (0 day/week), the adjusted odds ratios (AORs) (95% confidence interval) were 1.04 (0.92-1.19) for exposure to SHS at home from inside home for 1-4 days/week and 1.22 (0.99-1.51) for 5-7 days/week. The corresponding figures were 1.16 (1.01-1.32) and 1.48 (1.07-2.04) for exposure to neighbourhood SHS, 1.44 (1.26-1.64) and 1.21 (0.84-1.77) for exposure to THS at home, and 1.02 (0.93-1.12) and 1.27 (1.08-1.49) for exposure to SHS outside home.

Among all different SHS and THS exposure combinations, in both crude and adjusted models, exposure to more sources of SHS and THS was generally associated with higher odds of respiratory symptoms. Exposure to all 4 sources of SHS and THS was associated with an AOR of 1.86 (1.40-2.45) for respiratory symptoms.

In ever smoking primary students, the sample size was too small to generate consistent results and most AORs were non-significant due to the low smoking prevalence.

Conclusions: Respiratory symptoms were significantly associated with exposure to secondhand smoke at home from neighbours, thirdhand smoke at home and secondhand smoke outside home in Hong Kong never smoking primary school students.

This study was the first to research the association of SHS exposure from neighbours with respiratory symptoms among children in Hong Kong and a strong association was observed. The association between SHS exposure and respiratory symptoms may be underestimated if the exposure from neighbours was ignored. These results support more stringent smokefree policies in Hong Kong.