Characteristics of low, moderate and high severity trauma hospitalisations in a health region of Aotearoa New Zealand—10-year review

Trauma is a significant public health concern and a major cause of death and disability across the globe^1,2 and in Aotearoa New Zealand.³ Road traffic injuries are the leading cause of death for children and young adults aged 5–29 years and one of the major contributors to increasing disability.⁴ Aotearoa New Zealand has a relatively high burden of disease (as measured in Disability‑Adjusted Life Years [DALY]) compared to an average of other high‑income countries⁵ and road injuries, falls and self-harm were among the top 10 causes of DALY.⁴ Over 50,000 people are hospitalised annually due to injury, with an estimated economic cost of NZ$10.2 billion per year in Aotearoa New Zealand.⁶ In the 2016 injury-related health loss report, the Aotearoa New Zealand Ministry of Health (MoH) stated that an estimated 8% of total health loss from all causes was due to injuries.⁷ The 2021/2022 annual report of the New Zealand Major Trauma Registry (NZMTR) shows that transport was the most common mechanism of severe trauma presentations and was responsible for 48% of all severe trauma presentations nationally.⁸ However, limited information is available about the incidence of injuries and its potential to cause death and disability.⁹ Equitable use of resources for the prevention and treatment of injuries depends on the use of reliable and representative information on incidence rates and risks across ethnicities and demographic groups in the Aotearoa New Zealand context.

The Te Manawa Taki Trauma System (TMTTS) was established in 2010 to coordinate improvements in the quality of trauma care delivery within the Te Manawa Taki/Midland health region of Aotearoa New Zealand and served a population of 1,007,405, 28% of whom identify as Māori.^10,11 The Te Manawa Taki Trauma Registry (TMTTR) has been operating continuously since 2012, capturing comprehensive patient data across all age groups and injury severities, including time and date stamping of transfer of patients to and between six hospital facilities (Waikato, Tauranga, Whakatāne, Rotorua, Taranaki and Tairāwhiti Hospitals). This dataset is unique in Aotearoa New Zealand, and over 6,000 trauma patients are admitted to hospitals in the region annually.¹² It captures interventions and inpatient costs to allow detailed clinical outcomes and process evaluation. The TMTTR now holds over 90,000 Te Manawa Taki (TMT) trauma patient admission records. These data provide a reliable platform for evidence-based system analysis and population-based studies. Continuous monitoring and performance feedback enable improvements to service delivery and patient outcomes.¹¹ The TMT health region has broad demographic characteristics for age groups, ethnicities and rurality that are representative of Aotearoa New Zealand as a whole.^13,14

The aim of this research is to describe the incidence and characteristics of injuries resulting in admission to hospitals in the TMT region of Aotearoa New Zealand. Additionally, this study assesses associations between injury severity and cause of injury, length of hospital stays and cost. To our knowledge, this is the first study examining the characteristics of patients of all age groups and severities admitted to hospitals in a health region of Aotearoa New Zealand following trauma over a prolonged period (10 years).

Methods

A retrospective analysis of high-, moderate- and low-severity trauma data from the TMTTR identified patients of all ages admitted to TMT hospitals with an injury during the 10-year period from 1 January 2013 to 31 December 2022. Consistent with trauma registries internationally, patients were excluded if they sustained insufficiency or periprosthetic fractures, exertional injuries, hanging/drowning/asphyxiation without evidence of external force, poisoning, ingested foreign body, injury as a direct result of pre‑existing medical conditions or late effects of injury, or the injury occurred more than 7 days prior to admission.¹⁵ Demographic and injury event information in the trauma registry was collected from prehospital records, hospital systems and, where required, directly from patients. The cause and place of injury were classified by the International Classification of Disease (ICD-10-AM).¹⁶ The Abbreviated Injury Score (AIS), which is an anatomical scoring system used to grade the severity of individual injury on a scale of 1 (minor) to 6 (unsurvivable injury), is used by the registry to quantify injury patterns and severity.¹⁷ The TMTTR employs AIS Version 2008 for all diagnoses and for this review, trauma severity was split into high (ISS [injury severity score] >12),¹⁸ moderate (ISS 9–12) and low (ISS 1–8) severity trauma. ISS groups of low, moderate and severe were chosen to show variation in the characteristics of patients in the transition from the comparatively large “non-major” trauma group to “major” as defined in the NZMTR.¹⁹

The variables of interest included: patient demographic characteristics; injury event information; type, intent, cause and place of injuries; patient length of stay (LOS); outcomes; and direct cost to TMT hospitals. Multiple ethnicities were managed using prioritised ethnicity. The National Health Index (NHI) was used, together with admission date and times, as unique keys to extract trauma-specific admission costings from each of the five district hospital costing systems. All costs are direct hospital costs prepared in accordance with the requirements and guidelines of the Common Costing Standards.²⁰ Life-stage groups were children (0–14 years), working age (15–64 years) and older persons (65+ years). Intent of injury is consistent with ICD-10-AM¹⁶ and is categorised as unintentional, inflicted by others or self-inflicted. The mean LOS was calculated at an event level. This means that the LOS from admission date–time to discharge date–time during each hospital admission was summed at a patient-level prior to the calculation of global means. Annual incidence per 100,000 population was calculated by incorporating annual population projections for the TMT region provided by the MoH to Health New Zealand – Te Whatu Ora Waikato (district health board [DHB] population projections 2018 update). Case fatality rate was calculated as the proportion of trauma patients who died while in hospital, including within the emergency department as a result of their injury, and excluding “medical deaths” not resulting directly from their injuries such as hospital-acquired infections (e.g., pneumonia, sepsis). Data were extracted from the TMTTR using DI Writer/Collector^TM. All statistical analyses were performed using RStudio 2023.06.0.²¹ Population-adjusted incidence rate ratio (aIRR) and associated p-values were calculated using negative binomial regression using population (at study midpoint) as offset, and, using log link, all aIRR calculations were performed in RStudio using the “MASS” package.²²

Ethical approval was deemed out of scope by the New Zealand Health and Disability Ethics Committee (HDEC) and research approval was provided under the locality authorisation process by the Health New Zealand – Te Whatu Ora Waikato Research Office (RD023079).

Results

From 1 January 2013 to 31 December 2022, 60,753 trauma patients were admitted to hospitals within the TMT region. Of these, 4,781 (7.9%) were high-severity trauma (ISS >12), 6,203 (10.2%) were moderate-severity trauma (ISS 9–12) and 49,769 (81.9%) were low-severity trauma (ISS 1–8). The demographic characteristics of these patients are shown in Table 1. Males were more likely to be hospitalised for any traumatic injuries than females.

View Table 1–6, Figure 1–3.

There were 537 deaths in hospital following trauma events, including all “medical” deaths primarily due to medical causes rather than the injuries sustained, and this reduced to 430 when medical deaths were excluded. The global case fatality rate (CFR) for all trauma events was 0.71% (n=430 [died] vs n=60,323 [survived]). High-severity trauma events had a CFR of 6.92% (n=331 [died] vs n=4,450 [survived]) compared to a CFR of 0.84% (n=52 [died] vs n=6,151 [survived]) in moderate and CFR of 0.09% (n=47 [died] vs. n=49,722 [survived]) in low-severity trauma. Table 2 represents how CFRs varied by severity over the 10 years. CFRs are somewhat similar for all severities over the period but noticed a slight drop in 2019 for severe trauma.

Table 3 represents the population-adjusted IRR for gender and ethnicity. The incident rates are higher for males than females and show statistically significant relationships between gender and having a low, moderate or severe injury score. The population-adjusted incidence rates for Māori are higher than the non-Māori group for low and severe injury scores and show a significant relationship in the ISS 1–8 and ISS >12 bands. Incidence rates of moderate trauma are similar for Māori and non-Māori.

The annual incidence of severe and moderate trauma increased steadily during 2013 to 2022, while the incidence of low severity has been variable over the study period (Figure 1). The incidence of severe trauma almost doubled from 35 per 100,000 population (95% confidence interval [CI] 24–48 per 100,000 population) in 2013 to 67 per 100,000 population (95% CI 51–83 per 100,000 population) during 2022. Moderate-severity trauma has also increased from an incidence of 53 per 100,000 population (95% CI 39–68 per 100,000 population) during 2013 to 80 per 100,000 population (95% CI 62–97 per 100,000 population) during 2022. The overlap of 95% CI in the incidence of the moderate and severe groups as in Figure 1 suggests that this change over the period is not significant. On the other hand, non-overlaps of CI for low-severity trauma incidence suggest a significant difference between low-severity trauma incidences with the other two groups.

The proportion of high-severity trauma admissions increased from 6.6% of all admissions during 2013 to 11.2% during 2022. Moderate-trauma admissions also increased slightly from 9.0% of admissions during 2013 to 12.7% during 2022. The proportion of low-severity trauma decreased from 84.3% during 2013 to 76.1% during 2022.

The mean ages of hospitalised cases were 45.9 years, 45.5 years and 36.7 years for severe, moderate and low severity, respectively (Table 1). The proportion of moderate and severe trauma combined increased markedly from 14 years onwards (Figure 2). Adults aged 50 and over had an increase in the proportion of moderate severity, while 75.9% were admitted with low severity. Paediatric trauma, with the exception of infants aged 0–1 year, was also dominated by low-severity trauma. Irrespective of the age group, the proportion of low-severity trauma among females was higher than their counterparts. In contrast to that, the proportion of moderate trauma of males was higher than females. Hospitalisations of females aged 75 years or older were higher than males.

Across all ages, Māori accounted for 29.73% (n=18,015) of all trauma events; however, this was highly skewed towards the ≤9 and 15–29 age groups and represented 52.2% of their total presentation.

When high-, moderate- and low-severity hospitalisations were compared, the proportions of trauma events by both primary injury type and injury intent were similar (Table 4). There were slightly more penetrating injuries among severe trauma compared to moderate- and low-severity cases. There were proportionately more self-inflicted injuries among those with high severity compared to both low and moderate. Low-severity hospitalisations had a higher proportion of burn injuries compared to high and moderate cases.

The most common cause of injury among all-severity hospitalisations was falls (n=23,687) while the most common cause for severe trauma was road traffic crash (n=1,441), accounting for 37.4% of the top five causes of injury (Table 5). The top five causes cover 66% of all events. Falls were the most common cause of injury among both moderate- and low-severity trauma admissions.

The most common place of injury among all-severity hospitalisations was home (n=23,572), and street and highway for severe trauma (Table 6). The home was the most common place of injury among both moderate- and low-severity trauma admissions. Most falls (52%) occurred at home.

From 2013 to 2022, 70,910 admissions to TMT hospitals resulted in a combined 271,155 days of in-hospital care. An average LOS for high-severity trauma patients of 11.2 days resulted in a combined 53,761 days in the hospital. A mean 3.5-day LOS across 57,605 low-severity admissions resulted in a combined 175,978 days in hospital (81%). During 2013, all-trauma admissions involved a total of 21,588 days of in-hospital trauma care. This grew annually to 31,680 days of in-hospital trauma care during 2022, an increase of 137% over 2013.

The average LOS in TMT hospitals across 2013–2022 for high-severity admissions was 12.2 days (standard deviation [SD] ±13.9). This does not include any time spent in a hospital outside the TMT region following an outward transfer and is thus likely to be a slight under-estimate. The mean LOS for moderate- and low-severity admissions was 7.7 days (SD ±7.9) and 4.5 days (SD ±4.7) respectively. The annual mean LOS for low-severity trauma patients varied little from 2013 to 2022 while mean LOS was slightly more variable for moderate- and high-severity trauma admissions (Figure 3).

From 2013 to 2022, the total direct cost to TMT in-hospital trauma care cost was approximately NZ$599.13 million. Of this, high-severity trauma cost approximately NZ$142.27 million (23.8%) while moderate- and low-severity cost approximately NZ$86.08 million (14.4%) and NZ$370.06 million (61.8%) respectively. Direct in-hospital costs increased 122% from approximately NZ$37.44 million during 2013 to approximately NZ$83.27 million during 2022 (based on 97% of patients cost). While the proportion and incidence of low-severity trauma have decreased over time, the annual cost of their in-hospital care has continued to grow.

Discussion

This is the first study to report the descriptive epidemiology of low-, moderate- and high-severity trauma patients admitted to hospitals across all ages within a health region in Aotearoa New Zealand over a 10-year period. Considering the need to reduce the significant biopsychosocial and economic impacts of traumatic injuries, identifying at-risk populations and risk factors allows us to understand patterns of trauma in more detail, and will support targeted strategies for injury prevention.

The study includes 60,753 trauma patients who were admitted to TMT hospitals over a 10‑year period, during which time the incidence of admissions of high-severity trauma grew steadily, possibly owing to an increase in transport-related events.²³ Study results also demonstrate that differences in trauma rates exist in TMT region by gender, ethnicity and age. Males showed higher incident rates than females in all severities, ranging from an aIRR of 1.67 for low-severity trauma up to an aIRR of 2.6 for high-severity trauma. Hence, males were hospitalised 2.6 times more than females due to severe trauma. This is consistent with data from the annual report (2021/2022) of the New Zealand Major Trauma Registry & National Trauma Network.⁸ Either this may possibly reflect a tendency to exhibit high-risk behaviour, or differences in work-related activities between genders, as well as other factors. However, across all age groups, the proportion of low-severity females was higher than their counterparts. This may possibly reflect the differences in activities between genders, as well as other factors. The results also show that actual hospitalisations of females aged 75 years or over were higher than males. This may possibly reflect a greater proportion of females surviving into older age.

Study findings indicate that age has an important relationship with severity. The proportion of moderate- and high-severity trauma increases steadily with advancing age from 14 years. These findings are consistent with the systematic review of Montoya et al.⁹ This steady increase suggests that consideration should be given to commencing prevention initiatives at an earlier age than has traditionally been the case. Paediatric trauma except for infants ≤1 years is primarily low severity, with approximately 92% of cases being ISS 1–8. However, paediatric trauma was dominated by low-severity trauma. The age group analysis also shows an increase in the proportion of moderate trauma among adults aged 50 years and over. One possible explanation may be that falls, which are very common among older adults, contribute significantly to this trend.^3,24 As a result, older adults are more likely to have worse outcomes than younger age groups.^3,9,24,25

The study results show that though the Māori accounted for less than a third of all trauma events, this was highly skewed towards the ≤9 and 15–29 age groups and represented 52.2% of their total representation. This may be due to the younger age structure of the Māori ethnicity. Results show statistically significant relationships between ethnicity and severity. The population-adjusted incidence rates for Māori are higher than the non-Māori group for low and severe injury scores. This is in line with the literature, which showed that Māori experienced higher major trauma rates than non-Māori.^8,9

The proportions of primary injury types within each high-, moderate- and low-severity band were relatively similar, with only slightly more penetrating injuries among high-severity trauma patients. High-severity trauma is dominated by road traffic crash injuries while low-severity trauma is dominated by falls. These results are in line with the international studies discussed in Montoya et al.’s review.⁹ It is also noted that most falls occurred at home. This aligns with previous work suggesting structural hazards for falls are common in Aotearoa New Zealand homes.^3,26

The results demonstrate that the sum of total in-hospital LOS increased by 137% during the study period, but the mean hospital LOS varied slightly, suggesting increasing trauma admission volume was the main driver of the increasing sum of total hospital LOS. The study results also show that the direct cost of trauma care to TMT hospitals increased by 122%, which might be attributable to an increase in trauma admissions.

The study is unique in that it utilises a continuously collected dataset that represents low-, moderate- and high-severity trauma patients hospitalised across all ages within a health region in Aotearoa New Zealand, including estimates of hospital cost. The TMT region is also representative of Aotearoa New Zealand as a whole in terms of demography; therefore, the findings may be applicable in some degree to Aotearoa New Zealand as a whole. The study findings need to be considered in light of some limitations. This study includes hospitalised patients and does not represent a population sample of all traumatic injuries because it does not include non-admitted persons, nor pre-hospital deaths from injuries. Another limitation is that ethnicity data obtained from the registry and national collections can differ from how a patient identifies, potentially leading to misclassification bias that can under-estimate incidence rate of Māori.²⁷

Conclusion

During the 10-year period reviewed, the incidence of admissions of high-severity trauma in the TMT region grew steadily and varied by gender, age and ethnicity. Males and adult age groups predominate in traumatic hospitalisations resulting in significant cost and public health burden. The significant relationships between gender, ethnicity and injury severity may suggest that some groups are more at risk of severe trauma events. The population-adjusted incidence rates for Māori and non-Māori (despite similar incidence rates for moderate injuries) are very concerning. The current work will be used to direct and support in-depth analysis of at-risk groups to improve services and help reduce this significant and potentially preventable burden on the health system, patients and the community.