Thomas J. Esposito and Karen J. Brasel
From the public health perspective, injury is not considered an “accident” but rather a disease, much like malaria, tuberculosis and other public health scourges, or cancer and heart disease. Injury, like other diseases, has variants such as blunt or penetrating. It has degrees of severity, rates of incidence, prevalence, and mortality that can differ by race and other sociodemographic factors. Injuries have a pattern of occurrence related to age, gender, alcohol and other drugs, and again, sociodemographic factors, among others.
When public health concepts are applied to this disease of injury, it, like the aforementioned public health diseases, can be controlled to a socially acceptable level. The first step, however, is to characterize the disease such that control strategies can be applied. Epidemiology is the study of patterns of disease occurrence in human populations and the factors that influence these patterns.1
Descriptive epidemiology refers to the distribution of disease over time, place, and within or across specific subgroups of the population. It is important for understanding the impact of injury in a population and identifying opportunities for intervention.
Analytic epidemiology, in contrast, refers to the more detailed study of the determinants of observed distributions of disease in terms of causal factors. The epidemiological framework traditionally identifies these factors as related to the host (i.e., characteristics intrinsic to the person), the agent (physical, chemical, nutritive, or infectious), and the environment (i.e., characteristics extrinsic to the individual that influence exposure or susceptibility to the agent). The environment can be physical or sociocultural.
It is the understanding of how these multiple factors interact to increase the risk of injury and their influence on injury outcome that exemplifies the epidemiological approach to the study of disease and injury. By studying patterns of occurrence across and within populations of individuals, one can learn how best to potentially mitigate them. The concepts of the public health approach applied to injury control seek to modulate factors related to the host and agent and/or their interactions within the environment utilizing a number of strategies. These strategies encompass engineering, education, the enactment and enforcement of laws, and economic incentives and disincentives.
Injuries can result from acute exposure to physical agents such as mechanical energy, heat, electricity, chemicals, and ionizing radiation in amounts or rates above or below the threshold of human tolerance.2The transfer of mechanical energy accounts for more than three quarters of all injuries.3 The extent and severity of injury is largely determined by the amount of energy outside the threshold of human tolerance. Both the exposure to energy and the consequences of that exposure are greatly influenced by a variety of factors both within and beyond individual or societal control.4
The public health approach as it applies to injury was first conceptualized by William Haddon in the late 1960s.2 He developed and promulgated a phase-factor matrix that incorporated the classic epidemiological framework of host, agent, and environment in a time sequence that encompasses three phases: pre-event, event, and post-event. Factors related to the host, agent, or environment in the pre-event phase determine whether the event will occur (e.g., motor vehicle crash). Factors in the event phase determine whether an injury will occur as a result of the event and the degree of injury severity. Factors in the post-event phase influence the outcome from, or consequences of, any injuries of any severity that do occur.
An example of the Haddon Matrix applied to an actual injury event is depicted in Table 2-1. The addition of potential control strategies to the matrix in a three-dimensional fashion results in an “injury control cube,” suggesting that injury prevention and control are not unidimensional or unifactorial and that the greater the number of sections of the “cube” that are addressed, the greater the control of the injury event (Fig. 2-1A). For example, gun control laws focus on only the agent, in the pre-event phase, using a legislative strategy (Fig. 2-1B). However, there are many other counter measures that can be applied in other phases and to the host or environment (Table 2-2). The public health approach to injury control will be detailed further in Chapter 3.
TABLE 2-1 Haddon Matrix Conceptually Applied to a Motor Vehicle Crash Incident
FIGURE 2-1 (A) Injury control “cube” graphic depiction—general concept.
(B) Positioning of gun control laws in the injury control “cube” model.
TABLE 2-2 The Ten Leading Causes of Death by Age Group and Rank
OVERVIEW OF EPIDEMIOLOGY IN THE UNITED STATES
Injuries rank fourth as a cause of death for all age groups in this country. It is the leading cause of death among children, adolescents, and young adults ages 1–34 (Table 2-3).5 In 2009 nearly 150,000 persons died in the United States as a result of an injury. This yields an overall death rate of 54.4 injury deaths per 100,000 population translating into over 400 injury deaths per day with nearly 50 of these being children. Approximately 8 of every 10 deaths in young people ages 15–24 are injury related and more deaths among the young ages 1–34 are attributable to injury than all other causes of death in that age group combined. Trends in annual rates of death due to the nine leading causes among persons ages 25–44 over time are shown in Fig. 2-2.
TABLE 2-3 Counter Measures Available for Controlling Firearm-related Injury
FIGURE 2-2 Trends in annual rates of death due to the nine leading causes of death in the United States for those age 25–44 (1987–2006). (From Centers for Disease Control and Prevention, Atlanta, Georgia.)
Specific trends for injuries over the past several decades show an overall decline in the death rate from unintentional causes primarily due to advances in traffic and work place safety. Intentional injuries, particularly those related to firearms, have fluctuated over the last decade. Homicide deaths are predominantly responsible for the fluctuations, as suicide deaths have remained relatively stable.
The societal impact of injury is further emphasized when comparing the total years of potential life lost before age 65 across the leading causes of death (Fig. 2-3). Intentional and unintentional deaths account for over 30% of the total years of potential life lost for all deaths occurring in that age range. Therefore, injuries account for more premature deaths than cancer, heart disease, or HIV infection.5
FIGURE 2-3 Comparison of years of potential life lost before age 65 stratified by disease/condition. (From Centers for Disease Control and Prevention, Atlanta, Georgia.)
Previously, trauma deaths were characterized as having a trimodal distribution.6 However, more recent studies suggest a bimodal pattern with a reduction in late deaths7,8 The majority of all deaths still occur within minutes of the injury, either at the scene prior to arrival of emergency medical services (EMS), en route to the hospital, or in the first hours of care. These immediate deaths are typically the result of massive hemorrhage or severe neurological injury. Many fatalities succumb primarily due to central nervous system (CNS) injury within several hours to several days of the event. Far fewer than in original studies now die of infection or multiple organ failure many days to weeks after the injury (Fig. 2-4 A and B).
FIGURE 2-4 (A) Temporal distribution of trauma deaths, excluding individuals who were found dead by police. (B) Temporal distribution of trauma deaths caused by blunt and penetrating injuries, excluding individuals who were found dead by police. (Reproduced with permission from Sauaia A, Moore FA, Moore EE, et al. Epidemiology of trauma deaths: A reassessment. J Trauma. 1995;38:185.)
Currently, even the best EMS and trauma systems are largely ineffective in preventing those deaths that occur at the scene of the incident. Efforts at preventing the occurrence of the injury event or reducing the severity of the injuries incurred by the incident will be the most effective means of reducing this large number of immediate deaths. Continued efforts at developing trauma systems that foster rapid and efficient means of triage and transfer to higher levels of care, and efforts at clinical and translational research in the area of trauma, hemorrhage, and infection will eventually serve to reduce the delayed and late deaths.
Deaths represent only one small aspect of the injury disease burden. Each year, over 1.5 million people are hospitalized as the result of an acute injury and survive to discharge. Another 28 million are treated and released from emergency departments (EDs) or urgent care centers.8 Fig. 2-5 depicts these statistics for 2004. Injuries account for an estimated 6% of all hospital discharges and 30% of all ED visits annually. Many of these nonfatal injuries have far-reaching consequences with potential for reduced quality of life and high costs accrued to the health care system, employers, and society. The estimated total lifetime costs associated with both fatal and nonfatal injuries occurring in any 1 year amount to over 406 billion dollars9,10 (Table 2-4).
FIGURE 2-5 Injuries in the United States, 2004. (From Centers for Disease Control and Prevention, National Center for Health Statistics, Atlanta, Georgia. Injuries in the United States; 2007 Chartbook, Figure 1.)
TABLE 2-4 Incidence and Cost of Injury in the United States, 2000
The costs associated with injury deaths account for a disproportionate share of total injury costs. Estimates show that deaths account for less than 1% of all injuries but account for 31% of total injury costs. The majority, or the remaining 69% of costs due to injury, is associated with nonfatal injuries. These costs include direct expenditures for health care and other goods and services purchased as a result of the injury. Direct expenditures account for approximately 30% of the total cost of injury. The value of lost productivity due to temporary and permanent disabilities is also taken into account and represents 41% of the total costs. It is often mentioned that these are merely the financial costs and do not take account the pain and suffering to the patients, their families and associates that are the sequelae of nonfatal injuries.
OVERALL INJURY PATTERNS BY AGE AND GENDER
Injury is a disease predominantly affecting young males. Seventy percent of injury deaths and over half of nonfatal injuries occur among males.3,5,8 In every age group except ages 0–9, the rate of injury death for males is more than twice as high as the rate for females. For nonfatal injuries, males are only 1.3 times as likely as females to be affected. This gender-related risk reverses after the age of 65 with females being 1.3 times as likely as males to suffer nonfatal injury in that age category.
The disease of injury has a bimodal distribution of mortality that peaks for both genders in the 16- to 40-year-old age group and then again in those older than 65 years of age. Persons under the age of 45 account for 53% of all injury fatalities (Fig. 2-6), just over 50% of hospitalizations, and nearly 80% of ED visits.3,5,8 Hospitalizations and ED visits also follow this pattern of a bimodal peak related to age and a predominance among the male gender.
FIGURE 2-6 Injury death and injury death rates by age, 2003–2004. (From Centers for Disease Control and Prevention, National Center for Health Statistics, Atlanta, Georgia. Injuries in the United States; 2007 Chartbook, Figure 3.)
The elderly, while being less likely to be injured, are more likely to be hospitalized or die from those injuries with a lesser degree of severity than their younger counterparts. The rate of injury death among persons age 65 and older is 113/100,000 population and for persons age 75 and older it is 169/100,000. The elderly are overrepresented in the pool of injury fatalities and hospitalized patients. Although representing only 3% of the U.S. population, those over the age of 65 accounted for approximately 26% of all injury deaths and 30% of all injury-related hospitalizations. The proportion of citizens over the age of 65 is projected to increase to nearly 20% by the year 2030.11 This has significant implications for the future of health care as over the next several decades it is expected that the elderly will account for approximately 40% of all injury deaths and hospitalizations.
PATTERNS OF INJURY BY MECHANISM AND INTENT
Injuries are typically categorized by their mechanism, intent, and place of occurrence. Mechanism refers to the external agent or particular activities that were associated with the injury (e.g., motor vehicle related, falls, firearm related, etc.). Intent of the injury is classified as either unintentional (often referred to as “an accident”) or intentional.
Injuries that are intentionally inflicted can be further subcategorized into interpersonal (e.g., homicide) or intrapersonal (e.g., suicide). Intent may not be always determinable. Injuries resulting from legal interventions and operations of war are typically classified separately as an “other intent” category.
The classification system most often used in describing the specific mechanism and intent of injury is the international classification of disease (ICD). This classification system was developed and promulgated by the World Health Organization and is now in its tenth edition.12,13 The E-Code, which is the acronym for external cause of injury code, provides detailed information about the circumstances associated with injury-related ED visits and hospitalizations. These codes are considered essential to the epidemiology of injury and its accurate study. They provide critical public health information for monitoring health status, setting injury prevention priorities, and developing and evaluating injury prevention programs at the local, state, and national levels. E-Codes are also useful for injury-related quality-of-care assessments (e.g., risk of falls among older persons) in the emergency care, hospital, assisted living/nursing care, and home health care settings. As an example, fall prevention (e.g., reducing fall-related hip fractures) is one of the priority areas for quality and patient safety initiatives relevant to the present-on-admission (POA) Codes required for billing by the federal government (Center for Medicare and Medicaid Services [CMS]).
E-Codes can also be useful for other quality initiatives associated with injury-related claims (e.g., motor vehicle crash-related injuries) that may assist CMS in making payment decisions. Hence, numerous professional organizations, including the American College of Surgeons Committee on Trauma, the American College of Emergency Physicians, the Emergency Nurses Association, and the National Safety Counsel, have published position statements to endorse the need for improving E-Coding in state mortality and morbidity data systems. They have also urged that the capture of at least three codes as part of the electronic health record that is being proposed by CMS be essential. Two of the E-Code fields can be used for coding the precipitating and immediate causes (e.g., the mechanism/intent of injury such as falls, motor vehicle traffic, fire/burn, cut/pierce, assault, self-harm, etc.) and one other field to delineate place of occurrence (e.g., home, street/highway, residential, institution, etc.).
The distribution of injuries by mechanism varies for deaths, hospitalizations, and ED visits. The two leading mechanisms of injury death are related to motor vehicles and firearms. Using 2007 statistics from the Centers for Disease Control and Prevention (CDC), it appears there were over 182,000 deaths caused by injuries.5 Approximately 46,000 of these (25%) were traffic related with just over 31,000 (17%) related to firearms. Another 23,000 (13%) were related to falls. In contrast, using 2008 statistics, of the nearly 30 million nonfatal injuries reported to the CDC, approximately 8.5 million (29%) were related to falls whereas approximately 4 million (14%) were traffic-related injuries. Less than 1% of reported nonfatal injuries were related to firearms. When all intents are considered, burns account for approximately 2% of all injury deaths and 1.4% of nonfatal injuries reported by the CDC.5
These differences in distribution by cause and class of injury underscore the lethality of injuries involving firearms and motor vehicles. Perhaps also emphasizing this point are statistics on intentionality of injury, which reveal that 93% of nonfatal injuries are unintentional whereas 68% of fatal injuries are unintentional.
Nearly 30% of all injury deaths are violence related. In 2007 over 18,000 deaths were a result of homicide (34% of all violence related deaths) and over 34,000 deaths were caused by successful suicide attempts (66% of all violent deaths).
Injury in the workplace also constitutes a not uncommon occurrence. A total of 5,071 fatal work injuries were recorded in the United States in 2008. This represents 3.6 fatal work injuries per 1,000,000 full-time equivalent workers.14 Overall, transportation-related incidents accounted for the majority (40%) of occupational injury deaths. Assaults and violent acts accounted for 16% of fatalities, contacts with objects and equipment 18%, and falls 13%. Ten percent of occupational-related deaths in 2008 were a result of homicide, with firearm-related fatalities compromising 80% of these homicides. Five percent of deaths were a result of self-inflicted injuries.
In addition to the fatalities associated with work-related activities, there were a total of 4.6 million nonfatal injuries recorded by the Bureau of Labor Statistics (3.9 cases per 100 workers).15 Seventy-one percent of these occurred in service providing industries and nearly half produced disability.
DISTRIBUTION OF INJURIES BY NATURE AND SEVERITY
Cataloging and analyzing the distribution of injuries by their nature and severity is important to efforts at establishing priorities for prevention as well as treatment and trauma system development. Several systems for classifying the nature and severity of injury exist and a number of these are described elsewhere in this textbook.
The international collaborative effort on injury statistics has published an injury diagnosis matrix that provides a uniform framework for using the ICD codes in categorizing injury diagnosis by the body region involved and the specific nature of the injury.16 The most prevalent source of national data on the nature of injury death is death certificate data. However, these data have significant limitations due to variations and inaccuracy in the diagnosis listed as cause of death, terminology, and reporting practices for injury by geographic region and over different time periods.17,18 The National Trauma Data Bank (NTDB)19 also provides some insight as to the nature, severity, and types of injuries encountered utilizing a nonscientific sample of trauma centers that voluntarily contribute data to the data bank. Some of what is known about the overall nature of trauma deaths is based on a limited number of studies conducted in selected geographic regions using coroners’ reports and autopsy records.20,21 These types of records, much like the death certificates that are often based upon them, are variable in completeness, accuracy, and utility. Although the results of autopsy studies vary, they do suggest a trend that implicates CNS injuries as the most common cause of injury death, accounting for 40–50% of the total number of deaths. The second ranking cause tends to be hemorrhage, accounting for an additional 30–35%.
More recent and reliable data from the CDC confirms that traumatic brain injury (TBI) is a serious public health issue in America.22 TBI resulting from many mechanisms poses a serious public health problem contributing to a substantial number of deaths and cases of permanent disability each year. Like other injuries, TBI can range from mild to severe with many of the mild cases going undiagnosed. An estimated 1.7 million TBI-related deaths, hospitalizations, and ED visits occur in the United States each year. As suggested by autopsy studies, TBI is a contributory factor in nearly one third of all injury-related deaths in the United States or about 52,000 deaths annually (Fig. 2-7).
FIGURE 2-7 Traumatic brain injury death rates in comparison to overall injury death rates stratified by age—United States, 2006. (From Centers for Disease Control and Prevention, Atlanta, Georgia.)
The distribution of all nonfatal injuries by nature and severity is somewhat different from that described for fatal injuries. Many injuries occurring each year affect isolated body systems and are associated with a low severity. Even among injuries that result in hospitalization, only one quarter have an Abbreviated Injury Scale (AIS)23 score of 3 or greater on a scale of 0–6.
Injuries to the lower and upper extremities constitute the leading cause of hospitalizations and ED visits related to nonfatal injury. They account for over half (56%) of all nonfatal occurrences and 47% of all injury hospitalizations.8,9Slightly over one third of hospitalizations for extremity injuries are for moderately severe to severe injuries as measured by an AIS score of 3 or more.9 For many of these injuries, recovery can be protracted and costly. Even optimal treatment can result in permanent impairment and disability.24–26
The second ranking cause of nonfatal injury hospitalization is head injury, accounting for 10–15% of total hospitalizations for injury.27 Mild head injuries are predominantly treated on an outpatient basis, comprising 2–5% of all injury-related ED visits.28 Nearly 80% are treated and released. However, these ED statistics may actually be an underestimate, as many mild head injuries may be treated at urgent care centers and private physician offices and therefore not counted in the statistics. Estimates of the total incidence of head injury vary widely and range between 152 and 367 per 100,000 population.29 Although the majority of head injuries are classified as mild, conservative estimates suggest that between 70,000 and 90,000 people survive a significant head injury that often results in long-term disability.30 Head injuries incurred as a result of recreational activities are also not uncommon.31–33Approximately 300,000 such injuries occur annually. The estimated average proportion of annual TBI stratified by external cause is noted in Fig. 2-8.
FIGURE 2-8 Estimated average percentage of annual traumatic brain injury by external cause—United States, 2002–2006. (From Centers for Disease Control and Prevention, Atlanta, Georgia.)
Spinal cord injuries account for a relatively small proportion of all nonfatal injuries accounting for an estimated 10,000–15,000 hospitalizations per year.34 Once again, motor vehicles are the major cause of these types of injuries with 30–60% being a result of traffic incidents. Falls follow closely accounting for an additional 20–30%. Approximately 5–10% of all spinal cord injuries are due to diving. The total burden of injury stratified by body region is depicted in Fig. 2-9.
FIGURE 2-9 Total of all injury burden stratified by body region. (From Centers for Disease Control and Prevention, National Center for Health Statistics, Atlanta, Georgia.)
DISTRIBUTION OF INJURIES BY GEOGRAPHIC LOCATION
The overall incidence and patterns of injury vary between urban and rural populations and across different regions of the country.3,8 Unintentional injury death rates are highest in rural areas, whereas homicide rates are several times higher in central cities compared to rural and suburban communities (Fig. 2-10). Injury death rates also vary by region of the country. Death rates for unintentional injury tend to be highest in the west and south, whereas suicide rates are highest in the west and homicide rates highest in the south. However, there is a substantial state-by-state and even county-by-county variation. To date, local data relating to nonfatal injuries are not uniformly available to examine trends by rurality or geographic region. The observed differences related to geographic location and population density may be a function of a number of confounding factors such as access to care, economic, or educational climate, to name a few. When these factors are controlled for, these geographic disparities can be less prominent, or nonexistent.
FIGURE 2-10 Injury death rates stratified by degree of urbanization. (From Centers for Disease Control and Prevention, National Center for Health Statistics, Atlanta, Georgia. Injuries in the United States: 2007 Chartbook, Figure 11.)
CONFOUNDERS OF INJURY ANALYSIS AND INTERPRETATION
There are a number of confounding factors that may influence results and, more critically, the interpretation and conclusions drawn from epidemiological analyses of injury. These include race, ethnicity, culture, socioeconomic status, access to health care, mental health, alcohol and other drugs, as well as others. Due to their number and multiplicity, adequate control for any or all is difficult at best. Hence, forethought and caution should be exercised in making generalizations regarding some epidemiological findings.
Although on the surface there may appear to be certain associations between race and injuries, particularly violent injuries, controlling for socioeconomic status, there is little disparity between races as perpetrators or victims of violence. For example, homicide rates have been shown to vary significantly by economic status (Fig. 2-11). Homicide rates for black males of age 15–24 show urban rates to be 96/100,000 population and in nonurban areas only 41/100,000.
FIGURE 2-11 Violence-related deaths stratified by per capital income and race.
Therefore, data that are stratified by race and Hispanic origin must be interpreted carefully. First, the number of people in the population that is used as the denominator in the calculation of the death rate generally comes from U.S. Census Bureau estimates and the characteristics of those who died used in the numerator generally stems from either the funeral director or the medical examiner. As a result, to the extent that race and Hispanic origin are reported inconsistently by the different data sources generating the numerator and denominator, rates may be biased. Second, bias in estimates by race and ethnicity also can result from undercounting of specific populations in the census, thereby potentially producing an overestimation of death rates.
Differences in health status by race and Hispanic origin also are known to exist and may be explained by factors including socioeconomic status, health practices, psychosocial stress and resources, environmental exposures, discrimination, and access to health care.35 As these factors are not routinely collected or controlled for, analysis of injury mortality and morbidity by race and ethnicity may lead to incorrect inferences. With specific regard to data on violence, estimates may be misinterpreted because attention may have been directed to the victim rather than to the perpetrator, for whom sufficient data are not routinely collected. The National Violent Death Reporting System (NVDRS)36,37 may improve this particular problem by attempting to acquire data, when possible, on the perpetrator as well as the victim.
Although this chapter emphasizes the concept of injury being a disease entity in and of itself, data suggest that for a significant number of trauma patients, injuries may be an unrecognized symptom of an underlying alcohol or other drug use problem. Therefore, it may be that injury is actually a comorbidity of the disease that is alcohol and substance use disorder. Nearly 50% of injury deaths are alcohol related. Traumatic injury accounts for roughly the same number of alcohol-related deaths as cirrhosis, hepatitis, pancreatitis, and all other medical conditions associated with excessive alcohol use combined. A multicenter study that included data on more than 4,000 patients admitted to six trauma centers demonstrated that 40% had some level of alcohol in their blood upon admission,38 when other drug use is included up to 60% of patients test positive for one or more intoxicants.38–40 Therefore, it is clear that alcohol and substance use must be considered in the epidemiology of injury as well as in the equation leading to effective injury control.
LEADING MECHANISMS OF MAJOR TRAUMA
Traffic-related incidents involving motor vehicles are the leading cause of injury death and rank second as a cause of nonfatal injury in the United States. It is the leader of all causes of death in the 1–34 age group. There were 44,128 traffic-related deaths in 2007 and over 298,000 hospitalizations in 2008 for these types of injuries. They also accounted for nearly 5 million ED visits.
Adolescents and young adults are at the highest risk for both fatal and nonfatal injuries due to motor vehicles. Their rates of death, hospitalization, and ED visits are approximately twice the rate for all ages combined. White males age 15–24 are at particular risk. For black males in that same age group, traffic-related injury death rank second as a cause of death behind firearm-related injuries. The elderly, age 75 and older, are also at relatively high risk for dying from motor vehicle incident-related injury.
Males are more than twice as likely as females to die from motor vehicle crashes. Males under the age of 45 are also more likely to be hospitalized as a result of motor vehicle-related injuries, although the gender differential is not as great as for fatalities. Males and females age 45 and older, in contrast, are equally likely to be hospitalized.
Determinants of injury occurrence and severity in a motor vehicle-related incident relate to speed of impact, vehicle crash worthiness and the use of safety devices and restraints including safety belts, air bags, and helmets. When used, safety belts have been shown to reduce fatalities to front-seat occupants by 45% and the risk of moderate-to-critical injury by 50%. Currently, safety belt usage rates in the United States range from 68 to 98% with a national average of 84% in 2009.41 The additional presence of an air bag in belted drivers provides increased protection resulting in an estimated 51% reduction in fatality rate.
Despite some success in reducing the role of alcohol in motor vehicle injuries, it remains a major factor in fatal crashes among adolescents and young adults. Approximately 50% of all traffic fatalities including the driver, occupant, bicyclist, or pedestrian have been found to have a blood alcohol concentration (BAC) of 0.08 g/dL or greater. The proportion of fatally injured drivers with elevated BAC varies with age. For all age groups, it has slowly declined over time but has remained unchanged in recent years (Fig. 2-12).
FIGURE 2-12 Fatally Injured Drivers with Blood Alcohol Level ≥0.08%—United States, 1982–2004. (From Centers for Disease Control and Prevention, National Center for Health Statistics, Atlanta, Georgia. Injuries in the United States: 2007 Chartbook, Figure 13.)
Also of note is distracted driving. Distracted driving is an increasingly recognized risk factor for traffic-related injuries and deaths, which may supersede impaired driving as a contributor to these injury incidents. The practice of distracted driving has become a dangerous epidemic on America’s roadways. In 2009 alone, nearly 5,500 people were killed and over 450,000 more were injured in distracted driving crashes. In that year, 16% of fetal crashes and 20% of crashes resulting in non-fatal injuries involved reports of distracted driving.41 This does not include injuries and deaths incurred by distracted pedestrians and bicyclists.
Distracted driving is not limited to the high profile activity of texting while driving but also includes other behaviors such as eating, grooming, reading (including maps and directions), or watching videos while driving. However, because text messaging requires visual, manual, and cognitive attention from the driver, it is by far the most concerning and risky distraction. It has been reported that one is 23 times more likely to be involved in a crash while texting and driving.
Legislation to ban texting while driving is currently in place or in process in many states and municipalities. At present, nine states, the District of Columbia, and the US Virgin Islands prohibit all drivers from using handheld cell phones while driving. Thirty-five states and D.C. ban text messaging for all drivers, with 12 of these laws being enacted in 2010 alone.
In 2007 there were 31,224 intentional and unintentional gun related deaths in the United States, which equates to approximately 86 deaths per day. The overwhelming majority of these deaths are intentional (98%) and related to violence, with only 2% being unintentional.5
Firearm-related deaths rank second as a cause of injury death over all ages in the United States being responsible for 17% of all injury deaths. More than half (57%) of all firearm deaths were suicide and an additional 40% were homicides.
Firearm-related injuries disproportionately affect males and younger people. Approximately 87% involve males. In the 15–34 age group, firearm-related death rates for males are nearly seven times that for females. Firearm-related injuries are the leading cause of death in black males ages 15–34. From a global and cultural standpoint, firearm-related mortality is eight times higher in the United States than other high-income countries in the world.
The majority of firearm-related deaths among males ages 15–34 in the United States (67%) are homicides. Suicide accounts for an additional 33%. Suicide in the elderly is also a significant problem with 3,895 firearm-related suicides among the elderly between ages 65 and 84 or greater. This represents 22% of all firearm-related injuries for both genders and all ages. Over 90% of the suicides in the elderly population were among males.
Data on nonfatal firearm-related injuries are not as complete; however in 2008, there were 78,622 reported nonfatal injuries caused by firearms. The majority were again intentional; however, 17,215 were determined to be unintentional (22%).5
Both fatal and nonfatal firearm injuries are estimated to account for approximately 9% of the 406 billion dollar overall cost of injury in 2006, or nearly 37 billion dollars.10 Close to 8 billion (22%) were related to direct medical costs and over 29 billion (78%) were related to productivity losses. In analyzing firearm homicides, the firearm used in well over 80% of cases, where firearm type was known, involved handguns. It is estimated that firearms of some type are present in about 38% of all U.S. households and carried by one in 12 students.42,43 Some studies suggest that those who live in homes that harbor guns are more likely to die from homicide and suicide in the home than are residents of homes without firearms.44,45 There is evidence to suggest that few firearm deaths in the home stem from acts of self-protection. It is reported that half of those murdered in the home knew their assailant. Less than 2% of homicides committed with a firearm are judged to be justifiable, that is, in self-defense. In one survey, results revealed an average of just under 110,000 defensive uses of guns each year compared to approximately 1.3 million crimes committed with a firearm.46
With regard to suicide and guns, firearms are the primary method of suicide in both males and females. Firearms are utilized in well over 50% of successful suicide attempts. Suicides are five times more likely to be committed in homes that harbor firearms. Ninety-two percent of suicide attempts utilizing firearms are successful in comparison to only 27% that employ poisons and 4% involving cutting or stabbing.
There were 23,443 fatal falls in 2007 and over 8.5 million nonfatal injuries that were a result of falls. The overwhelming majority of these were unintentional. Falls represent approximately 13% of all injury deaths. Falls account for over one third of all injury hospitalizations and one quarter of all injury-related visits to the ED.5
The greatest occurrence rate is witnessed in the younger and older age groups; however, the severity profile in the two groups is quite different. In children, falls are common but generally not severe or fatal. Falls are the leading cause of nonfatal injuries for all children ages 0–19. Approximately 8,000 children are treated daily in U.S. EDs for fall-related injury.47 This totals almost 2.8 million children each year. Less than 3% of these visits result in hospitalization. Approximately one half of all pediatric falls occur in the home and one quarter occur at school. Falls in children ages 0–4 years are most commonly from furniture or stairs. In older children, falls are commonly from standing and/or associated with recreational activities related to playground equipment, bicycling, or sports.
In adults of working age, most fatal falls are from buildings, ladders, and scaffolds. Falls on stairs increase in significance starting at age 45.3 Gender ratios for injury deaths in adults differ by mechanism. ED visit rates for falls are consistently higher for men up to the age of 44. From age 45 and older, this trend reverses and by age 65, ED visit rates and hospitalizations for falls in women are nearly three times those in men. This finding is consistent with the increased fracture risk in women after menopause and, specifically, those with osteoporosis.
In the elderly, falls are a significant cause of mortality and morbidity being the cause of death in 23% of injury deaths for those 65 and over and 32% of injury deaths in those 85 years of age and older. The death rate from falls after age 85 is over three times that for people age 75–84 years old. Falls are also the most common cause of nonfatal injury in the elderly, accounting for nearly 60% of injury-related ED visits and approximately 80% of injury-related hospitalizations for persons age 65 years and older. In the United States, one in five people over the age of 65 will sustain a fall annually. Of these, about one quarter will be injured and another quarter will restrict their daily activities for fear of another fall. Fractures occur in approximately 5% of falls. Risk for hip fractures from falls increases dramatically with age. The elderly over age 85 are 10–15 times as likely to sustain hip fractures as people age 60–65.48,49 The economic impact of falls in the elderly is sizable and estimated to reach nearly 55 billion dollars in 2020.50
Major risk factors for falls among the elderly include those related to the host (advanced age, anticoagulant medications history of previous falls, hypotension, psychoactive medications, dementia, difficulties with postural stability and gait, visual disturbances, cognitive and neurological deficits, or other physical impairment) and environmental factors (loose rugs and loose objects on the floor, ice and slippery surfaces, uneven flooring, poor lighting, unstable furniture, absent handrails on staircases) to name a few. The risk of falling increases linearly with the number of risk factors present, and it has been suggested that falls and some other geriatric syndromes may share a set of predisposing factors. All of these factors are potentially modifiable with combinations of environmental, rehabilitative, psychological, medical, and/or surgical interventions.51
There are a plethora of data available nationally52 and locally to define and research injury epidemiology. A number of these data sources have been used in the production of this chapter and are referenced. Although data on nonfatal injuries are not as comprehensive or robust as those on fatal injuries, significant improvement has occurred in recent years relating to the scope and quality of data collection. This has enhanced the understanding of the magnitude and significance of injury as a major public health problem.
Several of these databases provide information on several types of work-related injuries with a number of others focusing on injuries and injury deaths related to other unintentional and intentional injuries. Many are ongoing surveillance systems. This collective group of databases varies in scope and the extent to which they provide information on mechanism and intent, nature and severity, risk factors, health services use, costs, and health outcomes. Some are population based and some are not. Comprehensive data on fatalities are available from vital statistics data, although these data do not provide detailed information about the extent and nature of injury sustained.
Standardized data on nonfatal injuries treated in the ED, including those treated and released, transferred, or hospitalized are available from the National Electronic Injury Surveillance System—All Injury Program (NEISS-AIP).53The NEISS-AIP is a collaborative effort between the National Center for Injury Prevention and Control (NCIPC) and the U.S. Consumer Products Safety Commission (CPSC). This database acquires information on over half a million injury-related ED visits to a nationally representative sample of 66 hospitals on an annual basis. The NEISS-AIR is the most comprehensive database on all nonfatal injuries presenting to hospitals with EDs that is currently available. These data, together with injury mortality data, can be accessed through WISQARS (Web-based Injury Statistics Query and Reporting System), which is an interactive database system supported by the NCIPC.5
Injuries that result in hospitalization can also be obtained from both the National Hospital Discharge Survey (NHDS) and the Healthcare Costs and Utilization Project (HCUP-3)54,55 Although both these sources can provide detailed information regarding the nature and severity of injuries, treatment, and discharge disposition, they are limited in that codes for classifying the mechanism and intent of the injury are not routinely recorded. Although strategies exist for estimating distribution by mechanism and intent given incomplete data, the lack of uniform E-coding of hospital discharges as well as the exclusion of ED cases that are treated and released remains a significant impediment to the optimal use of these databases for studying the entire spectrum of injury epidemiology. Initiatives to rectify this situation, as mentioned earlier in this chapter, are currently being undertaken.
An additional confounder in the reliability and accuracy of these essentially administrative databases is the extent, prioritization, and accuracy of ICD coding. Also, it should be pointed out that these are only population based from the standpoint of the population of hospitalized patients. They do not capture all deaths and will not ever include patients with minor injuries not seeking treatment at hospitals.
Softer and perhaps more subjective data on nonfatal injuries not resulting in hospital admission or death are available from the National Health Interview Survey (NHIS),56 The National Ambulatory Care Survey (NAMCS), and the National Hospital Ambulatory Medical Care Survey (NHAMCS).57 The NHIS relies on self-reports of injury events, whereas both the NAMCS and the NHIS rely on data abstracted from injury-related visits to hospital EDs, hospital outpatient departments, and/or physician offices. These databases do generally include E-codes.
In addition to these sources of comprehensive data across all types and severities of injury, several sources of national data exist that are specific to a particular mechanism or intent. Examples include the Fatal Analysis Reporting System (FARS),58 the National Automotive Sampling System—General Estimates System,59 and the Crash Injury Research and Engineering Network (CIREN).60 Also worthy of note are the National Occupant Protection Use Survey (NOPUS), National Fire Incident Reporting System (NFIRS), the National Traumatic Occupational Fatality Surveillance System and the Survey of Occupational Injuries and Illness for Occupational Injuries, the National Crime Victimization Survey (NCVS) and the Uniform Crime Reporting System for Intentional Injuries (which excludes suicides and self-inflicted injuries),61 as well as the American Burn Association Burn Repository.62 These databases are particularly useful for monitoring injury rates specific to certain mechanisms and for identifying risk factors associated with their occurrence.
Less developed are the data systems that deal with violence-related injuries overall and firearm-related injuries in particular. NVDRS37 catalogues violent incidents and deaths, death rates, and causes of injury mortality. However, data are only provided from 16 states and are not nationally representative. There has also been some movement toward developing a data collection system similar to that developed for motor vehicle crashes, which would be an essential component to a nationwide effort at reducing the epidemic of violence currently being experienced in this country.63 The development of a national violent injury statistics system64 has initially focused on evolving a national reporting system for firearm-related injuries; however, it has since expanded to include deaths from all homicides and suicides, regardless of weapon type. The ongoing efforts to develop this reporting system have focused on collection of current data for use in planning and evaluating policies aimed at reducing violent deaths.
Of particular interest to trauma clinicians and clinical researchers are clinical databases. The most noteworthy of these is NTDB.19 This database is the largest aggregation of U.S. trauma registry clinical data ever assembled. Since its inception, nearly 4 million records have been amassed emanating from over 900 trauma centers of various levels. Despite the robust nature of this database, it only contains data from trauma centers that have voluntarily contributed data. This introduces a notable element of sample bias. Additionally, data completeness, accuracy, and validity, have been continuous concerns, which have been increasingly ameliorated over time. As a partial solution to these issues, the American College of Surgeons Committee on Trauma, which administrates the NTDB, has instituted the National Sample Program that specifically seeks more highly controlled data from a nationally representative sample of 100 Level I and Level II trauma centers in the United States. A number of research data sets containing highly scrutinized and reliable data have also been created for use by researchers.
Two additional phases of trauma care where data have been lacking are the prehospital phase and the post–acute care phase or rehabilitation. The National Emergency Medical Services Information System (NEMSIS)65 is the national repository that is being developed to store prehospital EMS data from every state in the nation. Since the 1970s, the need for EMS information systems and databases has been well established, and many statewide data systems have been created. However, these databases vary significantly in their ability to acquire patient and systems data and allow analysis at a local, state, and national level. Currently 26 states contribute to the NEMSIS database, which is being characterized as the National EMS Registry and utilizing the NEMSIS data dictionary. The registry now includes over 10 million records for 2008–2010. An additional 12 states are close to implementing a statewide EMS data collection system that will allow for contribution this registry. There is an increasing impetus due to initiatives from professional organizations and regulatory agencies to have prehospital run sheets and data systems be NEMSIS compliant, which will facilitate submission of consistent and valid data to the national database.
Information from the post–acute phase of care is essential to long-term clinical and financial outcome studies. The Uniform Data System for Medical Rehabilitation (UDSMR)66 catalogs data from rehabilitation hospitals nationwide for use in evaluating the effectiveness and efficiency of their rehabilitation programs. It provides the most comprehensive data available on rehabilitation patients across many diagnostic categories, including injuries. The database includes information on demographics, type of injury, length of stay, primary payor, and postinjury rehabilitation circumstances such as employment status, living situation and Functional Independence Measure (FIM), which is the most widely accepted functional assessment measure in use by the rehabilitation community. The FIM is an 18-item ordinal scale used with all diagnoses within a rehabilitation population.67 The USDMR has been used in at least one long-term study of motor vehicle crash outcomes and costs.68
National data can be used for drawing attention to the magnitude of the injury problem, for monitoring the impact of federal legislation, and for examining variations in injury rates by region of the country and by rural versus urban/suburban environments. They can also be useful in aggregating sufficient numbers of cases of a particular type of injury to analyze causal patterns and clinical or other outcomes on an individual or systems basis.69 Often, however, these national data are not appropriate for the same or other purposes or for developing and sustaining injury prevention programs at the state and local level. State and local data are more likely to reflect injury problems specific to the local area and therefore more useful in setting priorities and evaluating the impact of policies and programs in these more limited catchment areas. Additionally, local data are typically more persuasive than are national data in advocating to establish a policy or to achieve funding of injury control programs at the local level. Some of the previously described national databases do provide subsets of data at the state or even county level; however, many do not.
Availability, accuracy and completeness of local injury data varies substantially by state and county. Vital statistics and death certificate data are generally available for 100% of injury-related deaths. As previously discussed, however, these data are limited in the information they provide about the nature and circumstances of the injury, cause of death, and risk factors associated with the death. Medical examiner and coroner reports can be a useful adjunct to death certificate data, but once again, the completeness and quality of these data vary substantially from state to state. Autopsy rates are equally variable and are generally biased toward being performed in cases of suspected homicide.
State and local data on trauma hospitalizations are generally available from two principal sources, those being uniform hospital discharge data including the UB-04 along with its predecessor UB-9270 and hospital or system trauma registries. Hospital discharge data are predominantly administrative in nature, whereas trauma registry data are primarily clinical. Both types of databases have limitations, which have been alluded to previously. Trauma registries suffer from selection bias and generally inconsistent inclusion criteria as well as highly variable data integrity. In both types of databases, ICD coding is not uniform. Administrative databases in general are not useful in attempting to analyze clinical issues despite available methods to estimate injury severity using ICD codes.71 Both hospital discharge databases and trauma registries do not include information on trauma deaths that occur at the scene, in transport, or in the ED nor do they routinely include patients treated and released.
Specifically, in comparison to hospital discharge data, trauma registries typically include more detailed information regarding the cause, nature, and severity of the injury. Some trauma registries will also include data on deaths occurring in the ED. Trauma registries, for the most part, collect information only on “major trauma” patients, generally excluding those patients who survive but remain in the hospital less than 3 days. Again, this leads to sample bias of a small subset of all injured patients in a population. It is important to reemphasize that caution should be exercised in using these databases for describing the epidemiology of trauma as neither is population based.
Uniform data on trauma patients treated and released from EDs, hospital clinics, and physicians offices are generally less accessible on a county or state level. Other data sources, often available at the state and local levels that can be useful in studying the epidemiology of injury, include routinely collected information from EMS, police, fire departments, poison control centers and child protective surgery, among others.
The utility of existing data at the state and local level can be significantly enhanced by linking data across multiple data sources. Single data sources are often limited in their content or scope of coverage, or both. Techniques have been developed and are continually being improved to facilitate linkage of these databases to avoid the high costs of gathering new data.72 Several states have now linked hospital discharge data, vital statistics, police crash reports, and prehospital run sheet data to examine patterns and outcomes of motor vehicle-related crashes.73 Although these linkage strategies and methods present an enticing opportunity for facilitating both short- and long-term trauma research and evaluation, it should be noted that linkage for the sake of linkage and analysis for the sake of analysis serves no useful purpose. Appropriate data must be turned into relevant information, which is then used to answer pertinent questions about injury, epidemiology, treatment, cost efficiency, and prevention. Many of these questions can be answered adequately, and perhaps more appropriately and accurately, by analyzing a single database rather than employing sophisticated schemes of data linkage that are often complicated and costly.
In summary, injury imposes a heavy burden on society in terms of both mortality and morbidity along with its sizable economic burden on the health care system and society. Largely unrecognized is the fact that many fatal and nonfatal injuries are preventable and controllable using specific strategies guided by the analysis of injury epidemiology. Hence there is no societal level of tolerance, or perhaps intolerance, and fear of incidence as there is for HIV or West Nile virus and H1N1 influenza. Yet, these diseases contribute much less to the burden of public health disease than do injuries.
Risks of injury death vary by age and gender. The majority of injury deaths are unintentional, with elderly people at a particularly high risk of death from unintentional injuries. Considering intentional injuries, overall, suicide greatly exceeds homicides, but rates again vary by age, gender, and urban or rural residence. Mechanisms of injury death also vary be age. The risk of injury death on the job varies by occupation. From a global perspective, the United States compares less than favorably with other countries in terms of fatal injury, particularly those related to firearms (Fig 2-13).
FIGURE 2-13 Firearm and motor vehicle traffic injury death rates, males 15–34, 1992–1995 for selected countries. (Reproduced with permission from Annest JL, Conn JM, James SP. Inventory of Federal Data Systems in the United States. Atlanta, GA: National Center for Injury Prevention and Control; 1996.)
The risks of hospitalization for injury vary by age and gender with elderly women at particularly high risk. Teens and young adults have the highest rates of initial ED visits for injury with many of these injuries occurring around the home.
In total, injury deaths declined slightly during the 1985–2004 period with some variation by intent of injury. Injury mortality trends vary considerably by mechanism of injury. Some causes are on the rise with others declining or remaining essentially unchanged. Injury morbidity rates have demonstrated declining trends among all age groups except the elderly. Although certain assumptions or “profiling” may arise from the association of injury and certain mechanisms thereof, a number of confounding factors unrelated to racial origin have been outlined, which should dissuade broad generalizations that are unfounded. Alcohol and other drugs continue to be intimately associated with all types and mechanisms of injury.
In conclusion, although significant strides have been made in reducing the rate at which injury occurs, trauma remains a major public health issue. More efficient ways of treating injuries as they occur, or tertiary prevention, should and will continue to be the major thrust of clinical care providers and researchers. However, it is equally important that efforts to develop appropriate programs and policies that will prevent them from occurring, that is, primary and secondary prevention also be prioritized. Education of policy makers and the public that this public health epidemic can and must be controlled is also an essential component of this effort.
Taken as a whole, integrated efforts at primary, secondary, and tertiary prevention, along with public information and education programs, are the only effective means to effect injury control and reduce the burden of injury on individuals, the health care system and society at large.74 Accurate and comprehensive data are essential to these collective efforts. Studying the epidemiology of injuries provides the opportunity for understanding how, when, and with whom to intervene.
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