ArticlesIncidence of traumatic brain injury in New Zealand: a population-based study
Introduction
Traumatic brain injury (TBI) is the leading cause of long-term disability in children and adults younger than 35 years,1, 2, 3 and has serious effects on the lives of patients, their families and friends, and society.4, 5, 6 An estimated 10 million people worldwide are affected every year by a new TBI event.3 Projections indicate that TBI will become the third largest cause of global disease burden by 2020.7 In the USA, an estimated 1·7 million people sustain a TBI annually,8 and about 5·3 million people live with a disability related to TBI.1 The incidence of TBI is estimated to be 200–558 per 100 000 population,9, 10, 11 with estimated overall economic cost in 2000 of about US$406 billion.12
Previous estimates of TBI incidence have been mainly based on official statistics (eg, patients admitted to hospital for TBI) and were prone to diagnostic and selection biases.13, 14 The true incidence of TBI is widely acknowledged to be higher than available estimates,3, 15, 16 because 70–90% of all TBIs are mild,4, 16 with only a small proportion of those affected by TBI being admitted to hospital.14, 15, 17, 18 However, even so-called mild TBI can result in long-term deficits.19, 20, 21, 22 Indeed, the National Institutes of Health declared in 1999 that mild TBI is a major public health problem,2 emphasising the importance of capturing the true burden of TBI in the population.15, 23 Available evidence also suggests ethnic inequalities in TBI incidence and outcomes,24, 25, 26 but accurate community data for such disparities in TBI burden are scarce. TBI should, therefore, be studied in a population-wide context, providing more robust estimates of incidence, outcomes, and the true burden borne by various communities.3, 11, 27, 28, 29, 30, 31 We aimed to estimate age-specific, sex-specific, and ethnic-specific rates of mild and moderate to severe TBI in the Brain Injury Outcomes New Zealand In the Community (BIONIC) study—a large, population-based, TBI incidence and outcomes study undertaken in New Zealand during 2010–11.
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Study participants
The study population included people of all ages in a large geographical area in the central North Island of New Zealand, including the city of Hamilton (129 249 people, 98 km2) and the surrounding rural area (Waikato District, 43 956 people, 31 987 km2; appendix). In the study area, Europeans constituted 55% of the study population, Maori 20% (the indigenous population of New Zealand), Pasifika (Pacific Islands people living in New Zealand) 2%, and people of other ethnic origins 15%. By its
Results
Of the 1369 individuals with TBI, most were boys and men, individuals younger than 35 years (69% [943]), urban residents (74% [1008]), and of European ethnicity (61% [837], table 1). Most patients had mild TBI (95% [1298]). Moderate and severe TBI were most common in individuals older than 15 years (90% [64 of 71]); mild TBI was most prevalent in individuals aged 15–34 years (40% [523 of 1298]). A substantial proportion of patients with TBI (36% [487 of 1369]) did not present to hospitals at
Discussion
To our knowledge, this study is the first large population-based study to investigate TBI incidence across the spectrum of severity in all age groups in a geographical region with urban and rural populations. The most important finding of our study was that the incidence of TBI per 100 000 people per year (790 cases), especially mild TBI (749 cases), in New Zealand was substantially greater than in other high-income countries in Europe (47–453 cases)29, 39, 40 and North America (51–618 cases).3
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