Implications of case definition selection on traumatic brain injury trends: A controlled interrupted time-series analysis of North Carolina emergency department data.

Background: In 2015, the CDC removed unspecified head injuries from its TBI surveillance case definition, complicating the investigation of long-term morbidity trends. We examined the long-term impact of this change on quantifying statewide TBI incidence.

Methods: North Carolina emergency department (ED) visit records were obtained from 2012 to 2024 and classified based on the presence (S09.90+) or absence (S09.90-) of the ICD-10-CM code for "head injury, unspecified". Segmented Poisson regression was used to compare slope- and level-changes in monthly TBI visit counts.

Results: From January 2012 through September 2015, TBI visits increased at a rate of 14.9 visits per month. TBI visits dropped at the onset of COVID-19, and then rebounded after the relaxation of the state's stay-at-home-order; however, this trend was diminished under the S09.90- definition, with a difference of 75.9 (57.2-94.6) visits per month between the two definitions.

Conclusions: The presence of unspecified head injuries in the TBI surveillance case definition substantially altered statewide trends and their inclusion may better reflect injury burden.