Epidemiology of traumatic brain injury

Mark Faul*; Victor Coronado    Centers for Disease Control and Prevention, Atlanta, GA, USA
* Correspondence to: Mark Faul, PhD, MA, Centers for Disease Control and Prevention, 4770 Buford Highway, Atlanta, GA, USA. Tel: + 1-770-488-1276 email address: mfaul@cdc.gov

Abstract

Traumatic brain injury (TBI) is a leading cause of death, and in a recent analysis it was found that nearly one-third of all injury-related deaths in the US have at least one diagnosis of TBI (CDC-Quickstats, 2010). This chapter presents the burden of TBI as regards age group, gender, costs, race, emergency department (ED) visits, hospitalizations, and deaths. Injury trends over a 15 year period are examined. Rehabilitation estimates and disability estimates are also available. Through good epidemiology we can better understand the causes of TBI and design more effective intervention programs to reduce injury. Important sources of evidence for this chapter include mostly studies from the US because of their leading work in the epidemiology of this important injury.

Key words

Traumatic Brain Injury

costs

mechanism

race

emergency department

hospitalizations

deaths

Alzheimer

rehabilitation

disability

trends

Overview: importance of injury and traumatic brain injury

In 2009, injury was the leading cause of death in the US for persons aged 1-44 years (CDC, 2009). Because the burden of injury is concentrated among these younger and middle age groups, the impact on disability-adjusted life years lost for injury is approximately 15% in the US. Meanwhile, the impact of injury on mortality for all age groups is approximately 10% (Murray and Lopez, 1997). Injuries are classified into the two categories of unintentional and intentional injuries, or violence-related injuries. For all age groups, unintentional injury is the fifth leading cause of death, after heart disease, malignant neoplasms, chronic respiratory disease, and cerebrovascular disease (CDC-WISQARS, 2009). After combining unintentional injury and violence-related injury, there were 177,154 total injury deaths in the US during 2009 (CDC-WISQARS, 2009). The most commonly injured body region associated with death was the head (Barell et al., 2002), and in a recent analysis it was found that nearly one-third of all injury-related deaths in the US have at least one diagnosis of traumatic brain injury (TBI) (CDC-Quickstats, 2010).

Overall traumatic brain injury rates

The overall incidence rate of TBI in the US for 2002-2006 was 579 per 100 000 persons, or approximately 1.7 million cases per year (Faul et al., 2010). This estimate includes all levels of TBI severity. The TBI-related hospitalization rate in the US was 93.8 per 100 000 persons. In a meta-analysis that included data from the 1990s and the 2000s, the TBI hospitalization rate in Europe was calculated to be 235 per 100 000 persons (Tagliaferri et al., 2005). However, methodological differences and variations in healthcare systems make comparisons of TBI rates across other countries challenging. Large variations of TBI rates are found among European countries (Berga et al., 2005). Most of the differences in rates were due to a broader admission criteria for mild TBI based on different case definitions and patient inclusion rules in Europe compared to the US (Berga et al., 2005). Meanwhile, TBI hospitalizations in Ontario, Canada, have been calculated as 22 per 100 000 persons for females and 52 per 100 000 persons for males during 2006-2007 (Colantonio et al., 2010). These differences are based mostly on a different definition of TBI (see more detailed information below). Because many developing countries experience a rapid surge during urbanization, which is associated with a rise in motor vehicle use, there is an increase in TBI-related motor vehicle crashes in those developing countries (WHO, 2006). The TBI incidence rate in developing nations is generally higher (e.g., India 160 per 100 000 persons and Asia 344 per 100 000, cited in Tagliaferri et al., 2005) than more developed nations and is predicted to surpass many diseases as a main cause of death and disability by the year 2030 (WHO, 2006).

Definitions

According to the US Centers for Disease Control and Prevention (CDC), a TBI is caused by a bump, blow, or jolt to the head or a penetrating head injury that disrupts the normal function of the brain. Not all blows or jolts to the head result in a TBI. Exposures to blasts, and the accompanying overpressure wave, are a leading cause of TBI for active duty military personnel in war zones (Champion et al., 2009). The severity of a TBI may range from mild to severe. Signs and symptoms vary by severity, ranging from loss of consciousness (LOC) lasting a few seconds to seizures, to coma, or even death. Much interest, however, has been placed on the lower severity spectrum of TBI, especially in cases who present with mild TBI (National Center for Injury Prevention and Control, 2003). The majority of reported TBIs in the US are classified as mild TBI (National Center for Injury Prevention and Control, 2003). Research suggests that up to 10% of persons with mild TBI may present persistent symptoms 1 year after the injury and in some cases even lifelong disability (National Center for Injury Prevention and Control, 2003). Patients with mild TBI may present with one or more of the following signs or symptoms: any period of observed or self-reported transient confusion, disorientation, or impaired consciousness; any period of observed or self-reported dysfunction of memory (amnesia) around the time of injury; observed signs of other neurologic or neuropsychological dysfunction, such as seizures acutely following head injury; infants and very young children may exhibit irritability, lethargy, or vomiting following head injury; symptoms among older children and adults such as headache, dizziness, irritability, fatigue, or poor concentration, when identified soon after injury, can be used to support the diagnosis of mild TBI, but cannot be used to make the diagnosis in the absence of LOC or altered consciousness (National Center for Injury Prevention and Control, 2003). Further research may provide additional guidance in this area. Any period of observed or self-reported LOC lasting 30 minutes or less can also be a symptom of TBI (National Center for Injury Prevention and Control, 2003).

Based on a clinical definition, the CDC has developed a standard TBI definition for surveillance purposes. This CDC definition is based on diagnostic codes from the International Classification of Disease (ICD) (Marr and Coronado, 2004). TBI is an outcome of an energy force transferred to the head according to the CDC definition. Forms of organic brain degeneration, such as those from congenital sources, stroke or anoxia, are not classified as a TBI (Traumatic Brain Injury Act, 1996). Although widely used, using administrative or billing ICD coded databases may not capture all cases of a particular condition, in this case TBI. The clinical diagnosis of a disease or injury is not always accurately reflected in administrative billing codes. The data used in the diagnosis of a TBI is more detailed and tends to be more accurate than the data used in a surveillance system. While a very specific diagnosis is of prime importance for treatment purposes, surveillance data systems tend to use multiple proxies as the goal is to get an estimate of disease burden. For example, in TBI, Bazarian et al. (2006) compared data obtained from emergency department (ED) medical records of patients with mild TBI to the corresponding data obtained from ICD coded billing records for services rendered in the ED; and found that the sensitivity, specificity, and positive predictive value of the ICD coded CDC definition for TBI was 45.9%, 97.8%, and 23%, respectively. These findings suggest that estimates based on these ICD codes do not completely capture mild TBI in an ED setting and that summary estimates should be viewed with caution.

Cost: burden of injury

The economic cost of TBI in the US is measured by combining the costs of two major cost categories (Finkelstein et al., 2006). The first is direct cost and includes the cost of deaths within and outside of the medical system and the costs of medical treatments of hospitalized and nonhospitalized TBI patients. The second category of cost is called productivity costs. Parts of these costs are lost wages and fringe benefits due to the incapacity to work and the absence from the workplace or disability from the injury. Simply stated, these costs represent a loss in value of what is being produced after a TBI. Using year 2000 data, the total annual cost of TBI was estimated to be 60.43 billion US dollars (Finkelstein et al., 2006). The direct cost of TBI was estimated to be 9.22 billion US dollars and the productivity losses were 51.21 US dollars. The productivity losses associated with TBI were higher than those associated with any other injured body region (e.g., other head/neck, spinal cord injury, vertical column injury, torso, upper extremity, lower extremity, other/unspecific and system-wide) (Fig. 1.1).