Incidence of traumatic brain injury in New Zealand: a population-based study

Background: Traumatic brain injury (TBI) is the leading cause of long-term disability in children and young adults worldwide. However, accurate information about its incidence does not exist. We aimed to estimate the burden of TBI in rural and urban populations in New Zealand across all ages and TBI severities.

Methods: We did a population-based incidence study in an urban (Hamilton) and rural (Waikato District) population in New Zealand. We registered all cases of TBI (admitted to hospital or not, fatal or non-fatal) that occurred in the population between March 1, 2010, and Feb 28, 2011, using multiple overlapping sources of information. We calculated incidence per 100,000 person-years with 95% CIs using a Poisson distribution. We calculated rate ratios [RRs] to compare the age-standardised rates between sex, ethnicity, and residency (urban, rural) groups. We used direct standardisation to age-standardise the rates to the world population.

Results: The total incidence of TBI per 100,000 person-years was 790 cases (95% CI 749-832); incidence per 100,000 person-years of mild TBI was 749 cases (709-790) and of moderate to severe TBI was 41 cases (31-51). Children (aged 0-14 years) and adolescents and young adults (aged 15-34 years) constituted almost 70% of all TBI cases. TBI affected boys and men more than women and girls (RR 1·77, 95% CI 1·58-1·97). Most TBI cases were due to falls (38% [516 of 1369]), mechanical forces (21% [288 of 1369]), transport accidents (20% [277 of 1369]), and assaults (17% [228 of 1369]). Compared with people of European origin, Maori people had a greater risk of mild TBI (RR 1·23, 95% CI 1·08-1·39). Incidence of moderate to severe TBI in the rural population (73 per 100,000 person-years [95% CI 50-107) was almost 2·5 times greater than in the urban population (31 per 100 000 person-years [23-42]).

Interpretation: Our findings suggest that the incidence of TBI, especially mild TBI, in New Zealand is far greater than would be estimated from the findings of previous studies done in other high-income countries. Our age-specific and residency-specific data for TBI incidence overall and by mechanism of injury should be considered when planning prevention and TBI care services.

Funding: Health Research Council of New Zealand.