The role of illicit THC vape carts in the lung injury outbreak –which has now caused 7 deaths–continues to become clear. Yesterday, Dallas County reported 14 new cases ranging in age from 16 to 44 with a median age of 19, all of whom were hospitalized with severe respiratory distress. Although the news headline mentions only that these cases were associated with “vaping,” if you read down to the 11th paragraph, you find out that “Ninety percent of the Dallas County cases reported vaping THC products.”
The CDC has continually downplayed the role of THC vape carts in the outbreak and even today, continues to blame it on electronic cigarettes generally. Most revealing is the fact that every time the CDC even mentions a potential role of THC, it immediately undermines it by emphasizing that “The investigation has not identified any specific e-cigarette or vaping product (devices, liquids, refill pods, and/or cartridges) or substance that is linked to all cases.”
The Rest of the Story
Don’t let the CDC fool you. What they’re not telling you is that in epidemiological outbreak investigations, we almost never identify a single exposure that ties together all of the cases. This is why we calculate odds ratios to estimate the strength of association between the exposure and the cases. If every single case was associated with a single exposure, then it wouldn’t take an epidemiological analysis to identify the source of the outbreak.
I defy you to find a single other CDC outbreak investigation in which the agency emphasized that “the investigation has not identified any specific exposure that is linked to all cases.” The failure to find a 100% link between a single exposure and every single case is the norm in outbreak investigations and never precludes the CDC from concluding that a highly common exposure is a likely source. Except in this investigation.
For example, consider the CDC’s investigation of an outbreak of severe ocular and respiratory illness following exposure to a contaminated hotel swimming pool. The investigation identified 24 cases of disease. What percentage of the cases had gone swimming or entered the pool area?
If you are thinking 100%, you are wrong. It was just 83%. But that didn’t preclude the CDC from concluding that the swimming pool was implicated in the outbreak. They didn’t issue a statement saying:
“While 83% of the cases reported spending time in the pool area, 17% did not. The investigation has not identified any specific exposure that is linked to all cases.”
Consider the CDC’s investigation of a Salmonella outbreak caused by contaminated beef sold in the U.S. Of the 73 cases who did not visit Mexico, what percentage reported eating beef?
If you are thinking 100%, you are wrong. It was 93%. Again, that didn’t cause CDC not to warn the public about the dangers of eating contaminated beef. They didn’t issue a statement saying:
“While 93% of the cases reported eating beef, 7% did not. The investigation has not identified any specific exposure that is linked to all cases.”
In the current outbreak investigation, there are many reasons why one would not expect to be able to tie every reported case to the use of THC vape carts:
1. The primary affected demographic group is youth. About half of the cases are ages 19 and below. Thus, many of the cases are minors and would be expected to under-report their use of illicit marijuana vape cartridges that by definition were obtained from black market drug dealers.
2. The CDC did not recommend that clinicians test patients for THC. In the absence of this testing, there is no way to validly conclude that a youth who doesn’t report using THC products actually did not use those products.
3. Not every youth may know exactly what is in the e-liquid cart they are using. It is entirely possible that some of the youths were vaping THC e-liquids but didn’t know it.
Frankly, given the consequences of admitting to illicit marijuana use for minors, it is quite remarkable that 90% the cases have admitted to using THC vape carts.
Given these basic principles of outbreak investigation, why would the CDC violate its own principles in an effort to try to implicate legal electronic cigarettes and to take the focus off marijuana vaping?
It is clear to me that the agency has a pre-existing bias against electronic cigarettes and really wants to be able to implicate these products.
The CDC might attempt to defend itself by saying that they are simply trying to be extra cautious. But the truth is that if they wanted to be cautious, they would immediately issue a very clear and explicit warning to youth not to vape marijuana, period. That they have failed to do this indicates that they are playing with children’s health and lives.
The rest of the story is that the CDC is playing with children’s health and lives in order to try to further demonize electronic cigarettes.
Michael Siegel, MD, MPH
Department of Community Health Sciences
Boston University School of Public Health
801 Massachusetts Avenue, 4th Floor
Boston, MA 02118