Popular E-Cigarettes Could Be Contaminated With Microbial Toxins

Electronic cigarette (e-cigarette) use has been on the rise in the United States in recent years. However, these products are still new, and little is known about the long-term health effects.

The US Food and Drug Administration reports that e-cigarette use “increased alarmingly” between 2017 and 2018. The 2018 National Youth Tobacco Survey found a 48% and 78% increase in e-cigarette use among middle school and high school students, respectively, from 2017 to 2018.

Now, investigators from Harvard T.H. Chan School of Public Health have determined that popular e-cigarette products sold in the US could be contaminated with bacterial and fungal toxins, which have been associated with asthma, reduced lung function, and inflammation.

The investigation conducted by the Harvard team was inspired by previous research experiences of senior author David Christiani, MD, MS, MPH, Elkan Blout Professor of Environmental Genetics in the Departments of Environmental Health and Epidemiology at Harvard T. H. Chan School of Public Health.

“I had studied airborne bioaerosols in the occupational setting for years, especially cotton textile workers, and found that exposure to airborne endotoxins resulted in chronic lung disease, specifically airway obstruction,” Christiani told Contagion® in an exclusive interview. “Other researchers have also reported similar findings. Since [e-cigarette] products contain constituents of possible agricultural origin (tobacco, cotton wicks, etc.), I wanted to assess the frequency and extent of possible contamination.”

According to a press release, Harvard research had previously discovered that chemicals with known associations to serious respiratory diseases were found in some e-cigarette flavors. Additionally, several decades of research have shown that exposure to airborne biological contaminants is linked to chronic lung impairment. However, this is the first time that investigators have explored the potential contamination of e-cigarettes with microbial toxins.

The results of this study were published online in Environmental Health Perspectives.

For the study, the research team examined 75 e-cigarette products, including 37 single use cartridges and 38 refillable e-liquids, from the top 10 e-cigarette brands in the United States. Each product was categorized into 1 of 4 flavor categories: tobacco, menthol, fruit, or other. Then, each product was screened for the presence of endotoxin or glucan.

The investigators found that 17 of 75 products (27%) contained traces of endotoxin and 61 of 75 products (81%) contained traces of glucan. Endotoxins are found on gram-negative bacteria and glucans are found in the cell walls of most fungi, which Christiani suggests adds to the concerns of potential adverse effects associated with e-cigarettes.

A detailed analysis found that cartridge samples had 3.2 times higher concentrations of glucan than e-liquids and glucan concentrations were “significantly higher” in tobacco- and menthol-flavored products when compared with fruit-flavored products. However, endotoxin concentrations were found to be higher in fruit-flavored e-cigarettes, which could indicate that the raw materials used to produce the flavors could be a potential source of microbial contamination.

The investigators cannot definitively identify the stage at which the contamination occurs but hypothesize that the cotton wicks that are used in cartridges of e-cigarettes may be a source of contamination, as Christiani’s previous research has determined that endotoxins and glucans are known to be “contaminants of cotton fibers.”

Christiani told Contagion® that future studies are needed to determine the clinical implications of this research and that an area of focus should be on human health responses to e-cigarette materials. “It is possible that given the presence of these [materials], there may well be inflammation of the bronchial tree and the potential for airway damage with obstruction if used chronically,” he said.

In a press release, Mi-Sun Lee, research fellow and lead author of the paper, pointed out that these results could be useful to health officials who are enacting policies to regulate e-cigarette use. "In addition to inhaling harmful chemicals, e-cig users could also be exposed to biological contaminants like endotoxin and glucan,” Lee said. “These new findings should be considered when developing regulatory policies for e-cigarettes."