# A population-based study of traumatic brain injury incidence and mechanisms in New Zealand: 2021–2022 compared with 2010–2011

## TL;DR

This study compares traumatic brain injury rates in New Zealand between 2021–2022 and 2010–2011, finding similar overall rates but shifts in who is affected and how injuries occur.

## Contribution

The study provides updated population-based TBI incidence data in New Zealand, highlighting changes in distribution over a decade.

## Key findings

- Total TBI incidence was 852 per 100,000 person-years, with males and urban residents at higher risk.
- Falls were the leading cause of TBI (48%), and their incidence increased significantly over the study period.
- Māori had a higher TBI risk compared to European and Asian populations.

## Abstract

Monitoring traumatic brain injury (TBI) incidence and epidemiological patterns is important for evidence-based strategic planning, policy, prevention, and resource allocation. We revisited population-based estimates and examined patterns of TBI incidence (all ages, severities) in 2021–2022 compared with 2010–2011 in New Zealand (NZ).

Examining an urban (Hamilton) and rural (Waikato District) region in NZ (May 2021–April 2022, unintentionally following the start of the COVID-19 pandemic), we calculated crude annual age-, sex-, ethnic-, urban/rural area- and mechanism-specific TBI incidence per 100,000 person-years with 95% Confidence Intervals (CI). Poisson regression was used to derive adjusted Risk Ratios (aRRs) to compare age-standardised rates between sex, ethnicity, and area groups. Direct standardisation was used to age-standardise rates to the world population. We calculated Incidence Rate Ratios (IRRs) with 95% CI to compare 2021–2022 with 2010–2011 age-standardised rates.

Total TBI incidence per 100,000 person-years was 852 cases (95% CI 816–890), including 791 cases (756–828) of mild TBI, and 61 cases (52–72) of moderate to severe TBI. TBI affected males more than females (IRR 1.31, 95% CI 1.29–1.33), and urban more than rural residents (IRR 1.57, 1.43–1.73). Most TBI (61%) occurred in people aged 15–64 years and were due to falls (48%). European and Asian peoples had lower risk of TBI than Māori (aRRs 0.68, 0.31 respectively). Compared to 2010–2011, total TBI incidence and rates among Māori were stable; TBI incidence was greater among females, urban residents, and adults aged ≥34 years; and TBI due to falls significantly increased (IRR 1.20, 95% CI 1.03–1.40).

Noting increased risks for underestimation due to COVID-19, findings suggest overall TBI incidence rate in NZ was similar in 2021–2022 to 2010–2011, while highlighting changes in TBI distribution. Age-, sex-, area-, ethnic-, and mechanism-specific distributions should be considered when revisiting prevention strategies to reduce TBI incidence.

10.13039/501100001505Health Research Council of New Zealand of NZ.