E-Cigarette Awareness, Use, and Harm Perception among Adults: A Meta-Analysis of Observational Studies

Objective
The aim of this study is to systematically review the published literature on the awareness, previous and current use, and harm perceptions of electronic cigarettes (e-cigarettes) among adults.
Methods
A search of the most current literature using the PubMed and Scopus database to identify articles published since 2003 yielded a total of 28 relevant articles.
Results
The pooled prevalence of awareness, previous use, current use of e-cigarettes and perceived healthier of e-cigarettes than regular cigarettes (healthier perception) among adults were 61.2% (95% confidence interval (CI): 51.5–70.8%), 16.8% (95% CI: 14.0–19.6%), 11.1% (95% CI: 9.2–13.1%), and 52.6% (95% CI: 42.5–62.6%), respectively, using a random effects model. The subgroup analysis showed that pooled estimates were highest in the group of current smokers of regular cigarettes, except that the highest pooled rate of current use was seen in the group of former smokers of regular cigarettes (the corresponding rates were 71.9% (95% CI: 57.5–86.3%), 27.2% (95% CI: 18.8–35.6%), 16.8% (95% CI: 7.2–26.3%), and 63.1% (95% CI: 52.1–74.1%)), and the lowest pooled rates were in the group of non-smokers, except for the rate of healthier perception in the users of e-cigarettes (and the corresponding rates were 46.8% (95% CI: 26.8–66.8%), 2.5% (95% CI: 1.1–5.6%), 1.2% (95% CI: 0.4–2.1%), and 37.9% (95% CI: -0.5–76.3%)). The cumulative meta-analysis found that awareness increased over time, while the prevalence of previous use, current use, and healthier perception first experienced an increase followed by a decrease and remained stable thereafter.
Conclusions
E-cigarette awareness has been increasing, and e-cigarette use and perceived health risks are nearly invariable between 2009 and 2014. Given the substantial heterogeneity in the prevalence rate estimates, there is a need for more accurate and comparable prevalence estimates for e-cigarettes across the world.