Sales of electronic cigarettes in the U.S. reached nearly $1.8 billion in 2013, but few of the smokers who tried the product have made the permanent switch from regular tobacco cigarettes, finds a new study published in the American Journal of Preventive Medicine.

E-cigarettes are battery-operated devices that heat a mixture of nicotine and flavorings and produce a vapor when inhaled. Some experts believe that offer a safe alternative to traditional tobacco cigarettes. However, it was unknown whether are using e-cigarettes in lieu of traditional cigarettes.

For the new study, a team of researchers led by Daniel Giovenco, a Ph.D. candidate at the Center for Tobacco Surveillance and Evaluation Research at Rutgers University, wanted to determine how many current and former smokers have tried e-cigarettes and whether they continued to use them.

Over 2000 current and former smokers were surveyed in June 2013 about whether they had ever smoked an e-cigarette or had become an "established users" (used e-cigarettes more than 50 times).

While nearly 47 percent had tried e-cigarettes, the number of established users was just 3.8 percent. Younger smokers between ages 18 and 29 and people living in areas with high cigarette taxes were more likely to have tried e-cigarettes. And while daily smokers were more likely to have tried e-cigarettes than former or , former smokers were 3.2 times more likely than daily smokers to be established users of e-cigarettes.

Giovenco and his colleagues call for improved methods for identifying established users who have adopted e-cigarettes, who may provide insight into product features or other factors associated with their sustained use.

More information: Giovenco DP, Lews MJ, Delnevo CD. Factors associated with e-cigarette use: a national population survey of current and former smokers. American Journal of Preventive Medicine. 2014.

Journal information: American Journal of Preventive Medicine