Estimating the global incidence of TBI

Keywords: TBI, incidence, RTI, road traffic injuries, road traffic accidents

Epidemiology of TBI

Traumatic brain injury (TBI) is one of the most important cerebral pathologies encountered nowadays, therefore, estimating the global incidence of TBI is o high importance. It is often referred to as the “silent epidemic” due to its contribution to global death and trauma-related disability. Each year there are about 500-800 new cases of TBI per 100,000 people, according to multiple studies from the United States and New Zealand. Unfortunately, there is an acute lack of data from low- and middle-income countries (LMICs). The prevalence of TBI, shown by a large survey-based study that enrolled patients from 8 LMICs, was estimated to be lower than 1% in China, whereas in Mexico and Venezuela was reaching about 15%. Most of these results approximate those from high-income countries (HICs). Consequently, there is a continuous need for efforts to identify as much as possible reliable epidemiological data on the incidence of mortality and disability from TBI in countries with resource-poor settings [1]. 

TBI represents one of the most important causes of mortality and morbidity in young people, and recent studies showed that their incidence is increasing, mainly in HICs, especially in people above 65 years old. The long-term disabilities that might appear due to brain injuries have a major impact on the survivor’s social life, daily activities, and also on their close family and friends. Studies showed that patients with TBIs have a lower life expectancy compared to the general population, and they also have increased mortality. The burden on the healthcare system is significant and showcased through direct and indirect costs [2].

Road Traffic Accidents and Road Traffic Injuries (RTI)

Road traffic accidents are one of the most essential sources of TBIs, especially in young people [1,2]. The Global Burden of Disease (GBD) Study in 2015 [3] managed to estimate the worldwide incidence of injuries due to road traffic, otherwise known as road traffic injuries (RTIs), based on population-based literature, using national registries and statistical modeling. The incidence of TBI can be estimated using the relationship between RTI and TBI. In order to ensure accurate TBI estimates, there is a need for a regional-specific estimate of their relationship, as the interaction between RTI and TBI most likely differs across regions with different regulations, populations, and infrastructures. 

Besides the disparity in data quality, it must not be forgotten that the majority of the population resides in LMICs, highlighting the need for more reliable sources and estimates for the burden of TBI in resource-poor settings. 

The study of Dewan et al. aimed to provide estimates for TBI across different geographic regions in different income groups in order to obtain a more realistic image of the global estimate of the burden and volume of TBI worldwide [1].

Estimating the global incidence of TBI in RTI

Several instruments are used to calculate the overall disease volume and incidence, as showcased in Figure 1.

Other research showcased a similar methodology for estimating the frequency of TBI in LMICs. Firstly, the incidence of RTI among different countries was obtained from the Institute for Health Metrics and Evaluation (IHME) GBD dataset. After that, the incidence of RTIs was converted to population-based rates P(RTI), which shows the proportion of RTIs in a given population. By multiplying these results, the P(RTI), by the country population, the researchers were able to obtain the total number of RTIs that occurred annually in a specific country. Further on, they tried to obtain the number of patients from the respective country that suffered a head injury (HI) or a TBI from total RTIs. Additionally, researchers aimed to obtain the proportion of TBIs caused by RTIs, considering that traffic accidents represent one of many TBI mechanisms of injury (MOI) [1]. 

Selecting the population

In order to obtain the proportion of the population that suffered an RTI yearly, scientists extracted relevant data on the incidence of RTI from the IHME GBD dataset using an open-access website [4]. IHME GBD data were excluded, while the World Health Organization (WHO), ministries of health, and regional offices were included in region-specific data sources. Also, the regions that were not recognized by WHO and WB, like Tibet, were excluded. Incidence data on both genders were selected for analysis over data showcasing information on just one sex. Also, sex and incremental age values were averaged, and mean incidence values were estimated for every country. Each incidence value was communicated as the probability that a person living in a specific country would sustain an RTI annually. The total number of RTIs per WB income group and WHO region was calculated as the product of the GBD RTI data and the WB 2015 population metadata. One must keep in mind that WB metadata are modeled figures used to project population changes over time. 

The probability of TBI following an RTI

To find the probability of sustaining a TBI after a road traffic accident, the ratio of road traffic accidents with TBI to all road traffic accident cases (with or without a TBI) in a population was determined by conducting a systematic literature search of PubMed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for studies reporting the proportion of road traffic accidents resulting in HI or TBI. This search aimed to identify hospital- and population-based studies that quantify injuries resulting from traffic accidents [3]. Only articles that mentioned different categories of injury resulting from road traffic accidents were included, and articles where the proportion of road traffic accidents resulting in head or brain injury was discernible. As a result, studies that included only HI or TBI and those that reported only a certain severity of the injury were excluded in order to minimize selection bias. 

Country Registry Screening

Moreover, a search of governmental traffic injury registries that reported cases of  HI was conducted. As a result, registries from 15 countries were screened: the United Kingdom, United States, Italy, France, Canada, Mexico, Brazil, Belgium, Chile, New Zealand, China, Taiwan, India, South Africa, and Australia. Only one registry (United Kingdom) contained compatible information on HI and was included in the model with the other peer-reviewed study data. The number of road traffic accident cases that resulted in TBI was calculated for all WHO regions and WB income groups [1].

Further analyses

A different meta-analysis and systematic literature review were conducted in order to estimate the proportions and relative distribution of the mechanism of injury (MOI) for TBI.  It aimed to calculate the proportion of TBI cases that could be attributable to road traffic accidents or the probability that a TBI was a result of a road traffic accident. Cochrane Database of Systematic Reviews and PubMed were searched using the PRISMA guidelines in order to identify studies that reported country-specific epidemiological data on the MOI of the TBI. A 6-point scale was used to score the methodological quality of individual studies, from lowest (0 meaning a small sample size, hospital-based) to highest (5 meaning large population-based) to compare the regions and income groups. Less rigorous study quality was allowed for studies from LMIC because otherwise, their data would have been unavailable. MOI studies were first selected on the basis of the completeness of data. After that, studies were reviewed for subject selection and study design. Studies that reported incidence within a population that could be extended beyond a hospital were also included for data analysis. MOI studies that had narrow selection criteria (e.g., only severe TBI, only pediatric patients, and so forth) were excluded [1]. 

The total number of TBI cases from all possible MOIs in a population annually was calculated, and the results were used in order to calculate the incidence of TBI in a given population. Researchers furthermore tried to characterize the distribution of severe, moderate, and mild TBI. The studies that were identified in the systematic review for the mechanism of injury were queried for the reporting of the severity of TBI. Population-based studies used the Glasgow Coma Scale in order to categorize TBI severity: 13-15 points for mild, 9-12 points for moderate, and 3-8 points for severe. TBI severity was calculated and multiplied by the total TBI incidence to arrive at an estimated incidence of severe, moderate, and mild TBI across income brackets and geographic regions [1].

Results

A total number of 66 countries were represented in the Global Burden of Disease road traffic accidents mean incidence rate data, including all WB income groups and seven WHO regions, as showcased in Figure 2.

The highest incidence was observed in the Southeast Asian Region, about 1,5%, and the lowest in the Region of the Americas-United States and Canada, about 1,1%. Even if the proportion of motor vehicle users across the WHO regions differs, there was minimal variability in the risk of road traffic accidents. 

A total of 12 large road traffic accident studies reporting data on the proportions of TBIs and His were found. Five WHO regions were represented: African Region (5 studies – 4 countries), Region of the Americas-Latin America (0 studies), Region of the Americas-United States and Canada (1 study), Eastern Mediterranean Region (0 studies), European Region (2 studies – 2 countries), Southeast Asian Region (2 studies – 1 country), (2 studies – 2 countries). 

Also, all income groups were Western Pacific Region represented. The most extreme proportions of road traffic accidents and TBI are highlighted in Figure 3.

Beyond epidemiology

Beyond epidemiological data, the patient demographics, the brain injury characteristics, and the study setting and design were captured in a large and comprehensive database of the most important and relevant TBI studies around the world over the last decade. After further filtering, 10 studies were identified, reporting on 11 unique cohorts that provided representative TBI mechanism distribution. A total of 6 studies that comprised 7 distinct cohorts were included in the severity of injury estimate. Severe TBI accounted for 7,95%, moderate TBI for 11,04%, and mild TBI accounted for 81,02%. 

The incidence of TBI was lowest in the African Region and highest in the Region of the Americas-United States and Canada, and the European Region. The global incidence of all-severity, all-cause TBI is estimated at 939 cases per 100,000 people. In conclusion, 69 million people worldwide will suffer a TBI each year. Mild TBI represents 740 cases per 100,000 people, a total of 55,9 million people each year, and 5,48 people will suffer a severe TBI annually. It is considered that somewhere around 64 to 74 million new cases of TBI occur annually worldwide, the majority of them being mild and moderate in severity [1]. 

The conclusion of this report should be examined in the context of the specific study design that the researchers used.

Conclusions of the study

In the study of Dewan et al., the most significant burden of TBI was seen in the Southeast Asian Region and the Western Pacific Region. However, the highest annual incidence of TBI was observed in the Region of the Americas-United States and Canada, and the European Region. Compared to high-income countries, healthcare systems in LMICs encountered almost 3 times more TBIs, but the results are limited to the low-quality data from these countries [1]. More attention and action need to be paid to the global disparity in healthcare between regions in order to obtain a lower disease burden worldwide. 

References

1. Dewan MC, Rattani A, Gupta S, Baticulon RE et al. Estimating the global incidence of traumatic brain injury. Neurosurg.2018. doi:10.3171/2017.10.JNS17352.
2. Majdan M, Plancikova D, Brazinova A, Rusnak M et al. Epidemiology of traumatic brain injuries in Europe: a cross-sectional analysis. Lancet Public Health 2016, 1, e76–e83. DOI: 10.1016/S2468-2667(16)30017-2
3. Global Burden of Disease Collaborative Network. Global Burden of Disease Study 2015 (GBD 2015) Life Expectancy, All-Cause and Cause-Specific Mortality 1980-2015. Seattle, United States of America: Institute for Health Metrics and Evaluation (IHME), 2016.
4. https://vizhub.healthdata.org/epi/