Association of Electronic Cigarette Use With Initiation of Combustible Tobacco Product Smoking in Early Adolescence.
OBJECTIVE
Exposure to nicotine in electronic cigarettes (e-cigarettes) is becoming increasingly common among adolescents who report never having smoked combustible tobacco.


OBJECTIVE
To evaluate whether e-cigarette use among 14-year-old adolescents who have never tried combustible tobacco is associated with risk of initiating use of 3 combustible tobacco products (ie, cigarettes, cigars, and hookah).


METHODS
Longitudinal repeated assessment of a school-based cohort at baseline (fall 2013, 9th grade, mean age = 14.1 years) and at a 6-month follow-up (spring 2014, 9th grade) and a 12-month follow-up (fall 2014, 10th grade). Ten public high schools in Los Angeles, California, were recruited through convenience sampling. Participants were students who reported never using combustible tobacco at baseline and completed follow-up assessments at 6 or 12 months (N = 2530). At each time point, students completed self-report surveys during in-classroom data collections.


METHODS
Student self-report of whether he or she ever used e-cigarettes (yes or no) at baseline.


METHODS
Six- and 12-month follow-up reports on use of any of the following tobacco products within the prior 6 months: (1) any combustible tobacco product (yes or no); (2) combustible cigarettes (yes or no), (3) cigars (yes or no); (4) hookah (yes or no); and (5) number of combustible tobacco products (range: 0-3).


RESULTS
Past 6-month use of any combustible tobacco product was more frequent in baseline e-cigarette ever users (n = 222) than never users (n = 2308) at the 6-month follow-up (30.7% vs 8.1%, respectively; difference between groups in prevalence rates, 22.7% [95% CI, 16.4%-28.9%]) and at the 12-month follow-up (25.2% vs 9.3%, respectively; difference between groups, 15.9% [95% CI, 10.0%-21.8%]). Baseline e-cigarette use was associated with greater likelihood of use of any combustible tobacco product averaged across the 2 follow-up periods in the unadjusted analyses (odds ratio [OR], 4.27 [95% CI, 3.19-5.71]) and in the analyses adjusted for sociodemographic, environmental, and intrapersonal risk factors for smoking (OR, 2.73 [95% CI, 2.00-3.73]). Product-specific analyses showed that baseline e-cigarette use was positively associated with combustible cigarette (OR, 2.65 [95% CI, 1.73-4.05]), cigar (OR, 4.85 [95% CI, 3.38-6.96]), and hookah (OR, 3.25 [95% CI, 2.29-4.62]) use and with the number of different combustible products used (OR, 4.26 [95% CI, 3.16-5.74]) averaged across the 2 follow-up periods.


CONCLUSIONS
Among high school students in Los Angeles, those who had ever used e-cigarettes at baseline compared with nonusers were more likely to report initiation of combustible tobacco use over the next year. Further research is needed to understand whether this association may be causal.
Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles2Department of Psychology, University of Southern California, Los Angeles.
Adam M
AM
Leventhal
Department of Family Medicine and Public Health, University of California-San Diego School of Medicine, La Jolla.
David R
DR
Strong
Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles.
Matthew G
MG
Kirkpatrick
Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles.
Jennifer B
JB
Unger
Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles2Department of Psychology, University of Southern California, Los Angeles4School of Social Work, University of Southern California, Los Angeles.
Steve
S
Sussman
Department of Human Development and Family Studies, Colorado State University, Fort Collins.
Nathaniel R
NR
Riggs
Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles.
Matthew D
MD
Stone
Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles2Department of Psychology, University of Southern California, Los Angeles.
Rubin
R
Khoddam
Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles.
Jonathan M
JM
Samet
Department of Psychiatry, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
Janet
J
Audrain-McGovern
D000293:Adolescent; D000294:Adolescent Behavior; D003625:Data Collection; D066300:Electronic Nicotine Delivery Systems; D005260:Female; D005500:Follow-Up Studies; D005731:Ganglionic Stimulants / Q000008:administration & dosage; D006801:Humans; D015141:Los Angeles / Q000453:epidemiology; D008297:Male; D009538:Nicotine / Q000008:administration & dosage; D016017:Odds Ratio; D012307:Risk Factors; D057566:Self Report; D012907:Smoking / Q000453:epidemiology*; D013334:Students; D062789:Tobacco Products / Q000706:statistics & numerical data*
D005731:Ganglionic Stimulants; D009538:Nicotine