Objectives: To provide updated estimates of the incidence of concussion from all causes diagnosed by all physicians in a large jurisdiction, as previous studies have examined only single causes of injury or from smaller specific populations. Design: Physician Billing and National Ambulatory Care Reporting System (NACRS) databases were used to identify all Ontario residents with a diagnosis of concussion (ICD-9 850.0 and ICD-10 S06.0) made by physicians between 2008 and 2016, excluding those with moderate to severe traumatic brain injury. Results: In total, 1 330 336 people were diagnosed with a concussion between 2008 and 2016. The annual average was 147 815, and 79% were diagnosed in the emergency department. The average annual incidence was 1153 per 100 000 residents. Incidence varied by age, sex, and geography; children younger than 5 years had the highest incidence of concussion, more than 3600 per 100 000 individuals of that age group. Males had higher incidence than females except in older than 65 years age groups. There was a Pearson correlation (+0.669) between sustaining a concussion and living in rural locations. Conclusion: The annual incidence of approximately 1.2% of the population is the highest rate of concussion ever reported thorough sampling methods and may represent a closer estimate of the true picture of concussion. Findings may inform future concussion treatment and healthcare planning.

Background Approximately 10% to 20% of people with concussion experience prolonged post-concussion symptoms (PPCS). There is limited information identifying risk factors for PPCS in adult populations. This study aimed to derive a risk score for PPCS by determining which demographic factors, premorbid health conditions, and healthcare utilization patterns are associated with need for prolonged concussion care among a large cohort of adults with concussion. Methods and findings Data from a cohort study (Ontario Concussion Cohort study, 2008 to 2016; n = 1,330,336) including all adults with a concussion diagnosis by either primary care physician (ICD-9 code 850) or in emergency department (ICD-10 code S06) and 2 years of healthcare tracking postinjury (2008 to 2014, n = 587,057) were used in a retrospective analysis. Approximately 42.4% of the cohort was female, and adults between 18 and 30 years was the largest age group (31.0%). PPCS was defined as 2 or more specialist visits for concussion-related symptoms more than 6 months after injury index date. Approximately 13% (73,122) of the cohort had PPCS. Total cohort was divided into Derivation (2009 to 2013, n = 417,335) and Validation cohorts (2009 and 2014, n = 169,722) based upon injury index year. Variables selected a priori such as psychiatric disorders, migraines, sleep disorders, demographic factors, and pre-injury healthcare patterns were entered into multivariable logistic regression and CART modeling in the Derivation Cohort to calculate PPCS estimates and forward selection logistic regression model in the Validation Cohort. Variables with the highest probability of PPCS derived in the Derivation Cohort were: Age >61 years (p^ = 0.54), bipolar disorder (p^ = 0.52), high pre-injury primary care visits per year (p^ = 0.46), personality disorders (p^ = 0.45), and anxiety and depression (p^ = 0.33). The area under the curve (AUC) was 0.79 for the derivation model, 0.79 for bootstrap internal validation of the Derivation Cohort, and 0.64 for the Validation model. A limitation of this study was ability to track healthcare usage only to healthcare providers that submit to Ontario Health Insurance Plan (OHIP); thus, some patients seeking treatment for prolonged symptoms may not be captured in this analysis. Conclusions In this study, we observed that premorbid psychiatric conditions, pre-injury health system usage, and older age were associated with increased risk of a prolonged recovery from concussion. This risk score allows clinicians to calculate an individual’s risk of requiring treatment more than 6 months post-concussion.

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