Susceptibility to cigarette smoking among middle and high school e-cigarette users in Canada.

There is a growing concern that the historic reductions in tobacco consumption witnessed in the past decades may be undermined by the rapid increase in e-cigarette use. This study examined the association between e-cigarette use and future intention to smoke cigarettes among middle and high school students who had never smoked cigarettes. Data were drawn from the 2014-2015 Canadian Student Tobacco, Alcohol and Drugs Survey (n=25,637). A multivariable logistic regression model was used to examine the association between e-cigarette use and susceptibility to cigarette smoking. In addition, an inverse probability of treatment weighted regression adjustment method (doubly robust estimator), which models both the susceptibility to smoking and the probability of e-cigarette use, was conducted. About 10% of the students had ever tried an e-cigarette. There were higher rates of ever e-cigarette use among students in grades 10-12 (12.5%) than those in grades 7-9 (7.3%). Students who had ever tried an e-cigarette had higher odds of susceptibility to cigarette smoking (adjusted odds ratio=2.16, 95% confidence interval=1.80-2.58) compared to those that had never tried an e-cigarette. Current use of an e-cigarette was associated with higher odds of smoking susceptibility (adjusted odds ratio=2.02, 95% confidence interval=1.43-2.84). Similar results were obtained from the doubly robust estimation. Among students who had never smoked cigarettes, e-cigarette use was associated with a higher susceptibility to cigarette smoking.