INTRODUCTION

Tobacco use often begins in adolescence¹. Today, the pattern of youth tobacco use has become more complex than ever before as alternative tobacco products (ATPs), such as electronic cigarettes (e-cigarettes) and waterpipe, gain increased popularity. From 2011 to 2014, waterpipe smoking has doubled and e-cigarette use has increased more than 5-fold among U.S. middle and high school students^2,3. In Poland⁴ and New Zealand⁵, e-cigarette use has tripled among school students. A common reason for ATP use is that young people perceive ATPs as less harmful and less addictive than cigarettes¹. However, ATPs may contain carbon monoxide, carcinogens and other toxicants^6-8. ATPs often contain nicotine⁹, and therefore, ATP use is associated with increased likelihood of nicotine dependence^8,10-12, especially when used concurrently with cigarettes^1,12.

ATP use often occurs in combination with cigarette smoking, but exclusive ATP use is also prevalent^13-15. Data from the 2012 U.S. National Youth Tobacco Survey showed that 14.6% of secondary school students were current (past-30-days) tobacco users, including 2.8% cigarette-only smokers, 5.3% exclusive ATP users, and 6.4% concurrent tobacco users (cigarettes and ATPs)¹⁶. Few studies have compared the characteristics of different types of tobacco users. Wickholm et al.¹⁷ compared cigarette-only smokers, exclusive snus users and concurrent users (cigarettes and snus) among Swedish boys and concluded that the rates of alcohol use and frequent binge drinking were highest among concurrent users and lowest among cigarette-only smokers. Cavazos-Regh et al.¹⁸ compared non-tobacco users, cigarette-only smokers, exclusive ATP users and concurrent users (cigarettes and ATPs) among U.S. adolescents and found that cigarette-only smokers and exclusive ATP users were no different in alcohol abuse disorders, but cigarette-only smokers were more likely to report marijuana and other illicit drug use disorders.

Information regarding other psychosocial factors related to the different types of tobacco users remains unknown. Moreover, ATP use has been insufficiently explored among Asian populations. Hong Kong, the most westernised city of China, has remarkably a low prevalence of daily cigarette smoking (10.5% in 2015 among residents aged 15 years or older)¹⁹. Smokeless tobacco products are prohibited for manufacture, importation and sale in Hong Kong²⁰. However, e-cigarettes have become increasingly available in retail stores, through social media and online stores²¹ and waterpipe lounges have spread widely in recent years²². E-cigarette use and waterpipe smoking are prohibited in statutory smoke-free areas²³. Waterpipe is regarded as a type of pipe by the Hong Kong Smoking (Public Health) Ordinance and subject to similar regulations including excise tax, health warnings and restriction of sale to people under 18 years old. However, enforcement of these regulations is uncertain and waterpipe smoking in waterpipe lounges is common²⁴. Flavored tobacco is often used for waterpipe smoking in Hong Kong²⁴ but the nicotine content of such products is commonly unclear and may not correlate with the plasma nicotine level of users²⁵. E-cigarettes containing nicotine are regulated as pharmaceutical products, which must be registered with the Pharmacy and Poisons Board of Hong Kong before sale and distribution. As of February 2018, no one has applied for a license to sell nicotine-containing e-cigarettes in Hong Kong. However, people can easily get nicotine-containing e-cigarettes through retail or online stores. Some e-cigarettes available on the market may be labeled as nicotine-free just to bypass the regulation. A recent study assessed the chemicals of 13 brands of e-cigarettes bought in Hong Kong and found that they contained nicotine at levels of 3.5–28.5 ng/mL²⁶. The low cigarette smoking rate and the increased availability of e-cigarettes and waterpipe in Hong Kong makes it a unique case to explore the different types of youth tobacco users and their characteristics.

In this study, we examined the prevalence of cigarette-only smoking, exclusive ATP use, and concurrent use of cigarettes and ATPs in a large representative sample of secondary school students in Hong Kong. We assessed the factors associated with exclusive ATP use and concurrent tobacco use compared with cigarette-only smoking. Findings may help improve our understanding about the characteristics of different tobacco users and help to develop tailored tobacco cessation interventions among adolescents.

METHODS

RESULTS

Table 1 shows the sample characteristics. Overall, 5.8% (95% confidence interval [CI]: 5.5–6.2%) of students reported current tobacco use, including 2.1% (95% CI: 2.0–2.3%) cigarette-only smokers, 2.5% (95% CI: 2.3–2.8%) exclusive ATP users, and 1.2% (95% CI: 1.0–1.3%) concurrent tobacco users. Waterpipe (1.2%, 95% CI: 1.1–1.4%) and e-cigarettes (1.1%, 95% CI: 1.0–1.3%) were the most popular ATPs used by students, followed by cigars (1.1%, 95% CI: 0.9–1.2%), chewing tobacco (0.8%, 95% CI: 0.7–1.0%), snus (0.6%, 95% CI: 0.5–0.7%), and nasal snuff (0.5%, 95% CI: 0.4–0.6%) and other non-cigarette tobacco products (0.4%, 95% CI: 0.4–0.5%; data not shown in Tables). Among current cigarette smokers (3.3% of all respondents), 35.0% reported concurrent ATP use; among ATP users (3.7% of all respondents), 39.0% reported cigarette smoking (data not shown in Tables). Compared with cigarette-only smokers, exclusive ATP users and concurrent tobacco users were: younger (p<0.001), mainly boys (p=0.001), students who perceived their family as being rich (p<0.001), those with no cigarette smoking peers (p<0.001), with poor knowledge about smoking (p=0.004), and those who consumed alcohol on ≥1 day/month (p<0.001).

Exclusive ATP use was associated with younger age (relative risk ratio, RRR=0.88 per year, 95% CI: 0.81–0.95), male (RRR=1.72, 95% CI: 1.27–2.34), perceived to be ‘rich’ (RRR=2.39, 1.55–3.68), absence of cigarette smoking peers (RRR=8.47, 95% CI: 5.03–14.27), poor knowledge about cigarette smoking (RRR=1.50, 95% CI: 1.12–2.01), and alcohol use on ≥1 day/month (RRR=1.56, 95% CI: 1.07–2.26), see Table 2. Similarly, concurrent tobacco use was associated with younger age (RRR=0.92, 95% CI: 0.84–0.99), perceived ‘rich’ (RRR=3.47, 95% CI: 2.20–5.47), having no smoking peers (RRR=4.66, 95% CI: 2.18–9.94), poor knowledge about smoking (RRR=1.65, 95% CI: 1.20–2.28), and alcohol consumption on ≥1 day/month (RRR=2.18, 95% CI: 1.37–3.46).

Among current cigarette smokers, ATP use was not associated with cigarette consumption each day (adjusted odds ratio, AOR=1.38, 95% CI: 0.99–1.91) or the time to first cigarette after waking up (AOR=1.38, 95% CI: 0.98–1.94), see Table 3. However, cigarette smokers who used ATP were less likely to have an intention to quit cigarette smoking (AOR=0.69, 95% CI: 0.50–0.97) and quit attempts in the past 12 months (AOR=0.67, 95% CI: 0.49–0.92) than cigarette-only smokers. Among cigarette smokers, concurrent use of ATPs was associated with perceiving themselves as being rich, having no cigarette smoking peers, poor knowledge about smoking, and drinking alcohol on ≥1 day/month.

DISCUSSION

This is the first study in Asia to compare the different types of tobacco users (i.e. cigarette-only smokers, exclusive ATP users, and concurrent users of cigarettes and ATPs) using a large representative sample of adolescents. It is among the few studies that examine the correlates of ATP use (exclusively and in combination with cigarette smoking) compared with cigarette-only smoking. ATP use (3.7%) was as prevalent as cigarette smoking (3.3%) among adolescents, with waterpipe and e-cigarettes being the most popular forms of ATPs²⁷. This finding is alarming. Emerging tobacco products, particularly waterpipe and e-cigarettes, usually target young people³⁰ and attract them with pleasant flavors and stylish designs. However, Hong Kong’s comprehensive tobacco control programs rarely discuss other forms of tobacco products. The prevalent ATP use in adolescents reflects the popularity of ATPs (particularly waterpipe and e-cigarettes) in the market, which may continue to expand with aggressive promotions. Policies prohibiting the use of flavors in all tobacco products and prohibiting the promotion and sale of all tobacco products to minors may help prevent the initiation of ATP use in adolescents. Surveillance systems should continuously monitor the use of all tobacco products. Prevention and intervention programs must address a wide range of tobacco products in addition to cigarettes.

Forty percent of adolescent tobacco users reported exclusive ATP use. It is of particular concern, as longitudinal studies among cigarette-naïve youth have found, that ATP use is a significant predictor of subsequent cigarette smoking^31-33. Another longitudinal study has concluded that e-cigarette use among never-cigarette smoking adolescents is predictive of future initiation of cigarettes, cigars and waterpipe³⁴. We also found that ATP use was prevalent among cigarette smokers, with 35.0% of cigarette smokers reporting concurrent use of ATPs. Concurrent use of cigarettes and ATPs may lead to increased cigarette consumption and the use of more different forms of tobacco products. A study of Danish adolescents has found that cigarette smokers who used waterpipe were more likely to report increased cigarette smoking intensity at follow-up than their counterparts who smoked cigarettes only³⁵. Saunders and Geletko³⁶ found that adolescent cigarette smokers who used one form of ATP were more likely to use other types of ATPs. More research is warranted to examine the trajectory of cigarette smoking and ATP use among Asian adolescents and to assess how the use of one form of tobacco product (i.e. cigarette or ATP) would affect the initiation and use pattern of other tobacco products.

Compared with cigarette-only smokers, exclusive ATP users and concurrent tobacco users were younger. This finding is in line with previous studies^37,38. Interestingly, relative to cigarette-only smoking, adolescents with higher perceived family financial status were more likely to report exclusive ATP use and concurrent tobacco use. It may reflect the different marketing targets as ATPs are usually more expensive than conventional cigarettes in Hong Kong. Researchers should better understand the marketing tactics of different tobacco products and how the marketing would affect youth’s perceptions about different tobacco products and their use patterns.

Relative to cigarette-only smokers, students with no cigarette smoking peers were more likely to report exclusive ATP use and concurrent tobacco use. It suggests that cigarette smokers and ATP users are two different communities despite some overlap between the two groups (35% of cigarette smokers and 39% of ATP users are concurrent tobacco users). A previous study found that peer use of non-cigarette tobacco products was correlated with ATP use among adolescent cigarette smokers³⁹. We had no information about peer ATP use in this study. Future research should assess peer ATP use and how it would influence youth tobacco use.

Poor smoking knowledge was correlated with exclusive ATP use and concurrent tobacco use. In Hong Kong, school-based anti-tobacco education programs focus on cigarette smoking and now include materials related to ATPs. The Survey did not measure students’ knowledge on ATPs. But the messaging on the negative health consequences of cigarette smoking appears to protect school children from using other tobacco products. Consistent with previous studies^17,40-42, we found that exclusive ATP use and concurrent tobacco use were associated with more frequent alcohol consumption. As noted in other studies, adolescent cigarette smokers who used ATPs were more prone to engage in other risk behaviors, such as drunk drinking⁴⁰ and illicit drug use^18,40,41, than cigarette-only smokers. Future tobacco control interventions for youth need to address alcohol use, collectively.

Notably, among cigarette smokers, ATP use was negatively associated with quit intention and attempt. It raises the concern that concurrent tobacco users may be less able to quit cigarette smoking than their peers who smoke cigarettes exclusively. Future tobacco interventions should address the use of all tobacco products and not just cigarette smoking.

Concurrent tobacco use was not associated with cigarette smoking intensity or the time to first cigarette after waking up. Potential reasons might be that many concurrent users in our sample used nicotine-free e-cigarettes or waterpipe, and that ATP use was infrequent. Our results are not in agreement with previous studies; Wang and colleagues⁴³ found that e-cigarette use in adolescent cigarette smokers was associated with heavier cigarette smoking intensity. Lee et al.¹⁶ and Post et al.¹² found that cigarette smokers who used ATPs were more likely to report tobacco use within the first 30 minutes of waking up. The contradictory findings might be explained by three factors. First, our study focused on a wider range of tobacco products, whereas previous studies focused on a single form of ATP (e.g. e-cigarettes⁴³ or snus¹²). Second, we coded the outcome of cigarette smoking intensity as a dichotomous categorical variable, whereas the prior study treated it as a continuous variable⁴³. Third, the adolescent populations were from different regions of the world¹². Further research is needed to examine if and how ATP use would affect nicotine dependence among Asian adolescents.

This study has several limitations. First, the cross-sectional study design limits the inferences about causality. Second, data might not be representative of all adolescents in Hong Kong as participants are school students (excluding special schools). Third, we have no information about the frequency and intensity of ATP use. Thus, we cannot determine whether the ATP users were merely experimenting with ATPs or established users. Fourth, the response rate at school level is low. However, we compared the characteristics of participating schools and students with Hong Kong Education Bureau’s data on schools and students; the small to medium Cohen’s effect sizes indicate that our findings are unlikely to be biased. Finally, the self-reported data are subject to recall and reporting bias.

CONCLUSIONS

This study has important implications for tobacco control practice. First, it demonstrates that the use of non-conventional tobacco products is as prevalent as cigarette smoking among adolescents, suggesting that tobacco control programs must address a full array of tobacco products in the surveillance, prevention and intervention efforts. Second, exclusive ATP users and concurrent tobacco users are different from cigarette-only smokers in many demographic and psychosocial factors, and ATP use is negatively associated with cigarette smoking quit intention and quit attempt. Health educators and tobacco cessation professionals need to develop tailored interventions for different types of tobacco users. Third, the significant clustering of tobacco and alcohol use suggests that tobacco prevention and intervention programs should address alcohol consumption, collectively.