Background:
Adolescent electronic cigarette (EC) use in relation to exposure to advertising has rarely been studied outside Western settings. We investigated the exposure to EC advertising in Hong Kong adolescents and its association with the intention to use ECs in never users.

Methods:
In 2014/15, 40202 Secondary 1-6 (US grade 7-12) students (mean age 14.9, standard deviation 1.8; 51.5% boys) from 92 randomly selected schools completed an anonymous questionnaire. Exposure to messages directly or indirectly promoting ECs through each of 12 sources in the past 30 days, and the intention to use ECs in the next 12 months or when a good friend offered an EC were reported. Weighted prevalence of exposure to EC advertising was calculated. Logistic regression yielded adjusted odds ratios (AORs) of intention to use ECs for the exposure to EC advertising (versus no exposure to any source) in never EC users.

Results:
In all students, 38.0% (95% confidence interval [CI] 37.5%-38.5%) were exposed to EC advertising, most commonly through television (15.1%). In never EC users (n=36274), any exposure to EC advertising was associated with an AOR (95% CI) of 1.50 (1.23-1.84) for the intention to use ECs, with increasing AORs for more sources of exposure (p for trend< 0.001) and an AOR of 2.20 (1.55-3.12) for 4 sources or more. Exposure through social networking sites (prevalence: 9.9%; AOR 2.58, 95% CI 2.03-3.27), video sites (4.4%; 2.56, 1.84-3.55) and other websites (2.5%; 2.26, 1.45-3.53) had the strongest associations with the intention to use ECs.

Conclusions:
Four in 10 Hong Kong adolescents were exposed to EC advertising through different sources. The exposure was dose-dependently associated with an intention to use ECs in never users. Banning EC advertising may prevent EC use in adolescents.