Background:
The harms of thirdhand smoking (THS) are being discovered, but limited studies investigated people's knowledge on these harms, especially in Asian population. Knowledge on harms of THS may increase support on tobacco control, as shown in the case of recognizing harms of secondhand smoking. We examined the association between knowledge on harms of THS and support on smokefree policies.

Methods:
In the Tobacco Control Policy-related Survey 2015 using random digit dialing, 902 of 1834 never smoking Hong Kong citizens aged 15+ were randomly selected to report their knowledge on harms of THS and support on smokefree policies. Respondents were asked if they agreed "THS increases risk of respiratory diseases in children". Respondents also indicated their support on an overall extension of smokefree zones and banning smoking in 8 different public areas. Adjusted odds ratios (AORs) from separate logistic regressions showed the associations between knowledge on harms of THS and support on smokefree policies in never smokers, adjusting for socio-demographic characteristics

Results:
Overall 81.0% respondents agreed "THS increases risk of respiratory diseases in children". Knowing harms of THS was associated with greater support on an overall extension of smokefree zones (AOR 2.13, 95% CI 1.32-3.45) and banning smoking in 7 out of 8 different public areas (AOR 1.86-3.42). The strongest association was found for public transport stops or waiting areas (3.42, 1.59-7.37), followed by outside seating of bars (2.91, 1.87-4.53) and all public areas in housing estates (2.75, 1.63-4.65).

Conclusions:
Knowledge on harms of THS was associated with greater support on smokefree policies. Future prospective studies should be conducted to investigate whether increasing never smokers' knowledge on harms of THS could raise their support on smokefree policies.


[THS harms knowledge & support on smokefree policy]