bi graphicsopioid death rates Skye Gould/Business Insider
A new investigation by a field officer for the Centers for Disease Control and Prevention indicates the actual number of deaths involving opioids, a powerful class of painkillers, may be much higher than official tallies.

In December, the CDC said 52,404 people had died from drug overdoses in 2015, with over 60% dying from opioids. That number has been rising for years.

But CDC field officer Dr. Victoria Hall and her Minnesota-based team recently reviewed a decade of death records submitted to the Minnesota Department of Health's Unexplained Death (UNEX) surveillance system, which keeps track of deaths for which no clear explanation is readily available.

Hall, who presented the results on Monday at a CDC conference. found that of the 1,676 UNEX deaths during that time period, approximately 3.5% had some complications due to opioid use. Those deaths were never filed as opioid-related deaths, despite some autopsies showing toxic or even lethal levels of painkillers.

"While my research cannot speak to what percent we are underestimating, we know we are missing cases," Hall told CNN. "It does seem like it is almost an iceberg of an epidemic."

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The problem comes in how the CDC classifies deaths using codes dictated by the CDC's International Classification of Diseases, Tenth Edition, or ICD-10. In some cases, if a person died due to an infectious disease, such as pneumonia, the death was classified for that only that condition, even if opioids were seen as a significant contributing factor.


The UNEX system, which began in 1995, was originally in numerous states; Minnesota is the only state to currently maintain its system.

While Minnesota is the only state that uses the UNEX system, it is likely the coding issue isn't limited to the state, according to Hall. There is no national standard for how to file a death certificate, according to Hall, or for what constitutes an overdose, leaving much to a medical examiner's discretion.

Minnesota is far from the hardest-hit state in the opioid crisis — ranking 45th in the US by overdose death rate. If the coding issue does turn out to be a national issue, as Hall suspects, the number of opioid-related deaths could spike dramatically.