EPIDEMIOLOGIC ASPECTS OF BRAIN INJURY
Section snippets
METHODOLOGIC ISSUES IN THE EPIDEMIOLOGY OF BRAIN INJURY RESEARCH
Although clinical aspects of brain injury have been studied widely, population-based assessments of brain injury are relatively new, and methodologies have not been standardized. A central issue in comparing various reports is that the phrase brain injury often has been used synonymously with head injury. For research purposes, however, the former should be considered a subset of the latter. Many injuries classified as head injury do not have associated neurologic involvement. Another
MORTALITY AND CASE FATALITY RATES
About 6.5% of deaths in the United States were attributed to injury causes in 1992.5 Assuming that 40% of these deaths were attributable to brain injury,27 there were approximately 56,000 brain injury deaths—an overall brain injury–associated death rate of about 22 per 100,000 per year. This rate has remained stable over the last 2 decades (D.M. Sosin, personal communication, April 1994).
In-hospital case fatality rates are one measure of severity for patient groups with the diagnosis of brain
HOSPITAL ADMISSIONS
The number of individuals admitted annually to hospitals for brain injury in the United States is not known, nor is it known for most other countries for which admission statistics are kept. The reason is similar to that for problems with using death certificate diagnoses: Brain injury may not have been the principal admission diagnosis. Hence, brain injury may be listed only after other more severe injuries. General estimates of brain injury hospital admissions may be derived using two
INCIDENCE STUDIES
Incidence rates of brain injury in the United States in the 1970s and 1980s have been estimated variously to be between 160 and 375 per 100,000 per year (Fig. 3).2, 14, 17, 23, 25, 28, 52 Although differences in brain injury incidence rates between rural and urban areas4 and between various ethnic groups are suggested, substantive methodologic differences between studies make comparisons difficult. The average US incidence rate of fatal and nonfatal hospitalized brain injury is about 237 per
EXTERNAL CAUSES OF BRAIN INJURY
Worldwide, the most frequent exposure associated with both fatal and nonfatal brain injury is transport-related causes.2, 14, 16, 17, 18, 23, 25, 28, 31, 52 This category includes accidents involving automobiles, trucks, bicycles, motorcycles, aircraft, watercraft, road farm equipment, and pedestrians struck by vehicles. The incidence of transport-related brain injury does not vary significantly among most studies. Significant differences with respect to specific subcauses are seen, however.
Age and Gender
The 15- to 24-year-old age group is at highest risk for brain injury. Younger persons, particularly those under age five, are at moderately high risk. Figure 4 illustrates age-specific brain injury incidence rates for a composite of four studies2, 17, 23, 52 and three additional individual studies.14, 25, 28 Individuals in their midlife years show consistently low rates, but these rates rise again after about age 60. The pattern reflects increased exposure in young adults to motor vehicle
PREDICTION OF OUTCOME
The issue of accurate prediction of outcome following brain injury has been addressed by many investigators. No single set of indicators has been demonstrated uniformly to be accurate in predicting outcome (Table 2). Thatcher et al47 found that electroencephalography and the GCS scores were excellent predictors of outcome if only the dichotomous outcomes of good recovery or dead were considered. Wa¨rme et al51 found that GCS motor score, systemic hypotension, and duration of hyperventilation
THE PUBLIC HEALTH IMPACT OF BRAIN INJURY PREVENTION
The worldwide incidence of brain injury may be as high as 500 million per year.2, 16 Only recently has the focus relevant to brain injury changed from clinical intervention to prevention. There is, however, a lack of reliable data to estimate the contribution of brain injury to the world's health burden so that reasonable priorities and strategies can be developed for primary and secondary prevention. A conceptual model of phases associated with primary, secondary, and tertiary brain injury
ACKNOWLEDGMENTS
We acknowledge with appreciation Swarup Sarkar, MD, and Bonnie Blander, BA, for their library research.
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Address reprint requests to Jess F. Kraus, MPH, PhD, Department of Epidemiology, Southern California Injury Prevention Research Center, School of Public Health, 76–078 CHS, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095–1772
Work on this article was supported by the Southern California Injury Prevention Research Center, funded by Centers for Disease Control and Prevention.
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From the Department of Epidemiology, Southern California Injury Prevention Research Center, School of Public Health, University of California Los Angeles, Los Angeles, California