TBI in the US: A Report to Congress

Traumatic Brain Injury in the United States:
A Report to Congress

CDC Estimates of Traumatic Brain Injury-Related Disability

Prevalence

The CDC's National Center for Injury Prevention and Control estimates that 5.3 million U.S. citizens (2 percent of the population) are living with disability as a result of a traumatic brain injury. This represents the prevalence of TBI disability, defined as the proportion of persons in the population at a given time who have disability resulting from a traumatic brain injury. To estimate the prevalence of disability from TBI in the United States, CDC developed a model incorporating data on the incidence of TBI, severity of injury, and likelihood of disability given a specific level of injury severity.22 Data come from several sources:

CDC estimated the incidence of TBI by using its case definition and 1970-1995 National Hospital Discharge Survey (NHDS) data, obtained from CDC's National Center for Health Statistics.

CDC estimated the severity of TBI by using NHDS data, classified according to ICD-9-CM-derived Abbreviated Injury Scale23 (ICD/AIS) scores by means of a computer algorithm (ICDMAP-90Š).

Calculating the likelihood of disability following TBI at each level of severity required two data sources. For injuries occurring in 1980 or after, CDC obtained preliminary follow-up data from the Colorado TBI Registry and Follow-up System,26 which surveyed TBI survivors one year after injury and measured disability by using the Functional Independence Measure.27 For injuries that occurred before 1980, we used historical data reviewed by Kraus.

The model uses these data to estimate the number of persons alive in 1996 who had ever had a TBI that required hospitalization and resulted in long-term disability. It incorporates differences in rates across age groups, variations in injury severity, and changing patterns in hospital admissions related to severity. The model does not account for disability among people who visited emergency departments or outpatient clinics with a TBI but were not admitted to the hospital. Because of this, our estimate of 5.3 million U.S. citizens living with TBI-related disability may be low. Other restrictions in existing data and methods may also affect the accuracy of this estimate.23 Given these limitations, some variation in future estimates of the prevalence of TBI-related disability is expected.

Incidence

According to NHDS data, the annual incidence rate of TBI hospitalizations has been declining since 1975, when it peaked at 234 per 100,000 population (500,000 cases). During 1990-1995, the mean annual incidence rate for persons hospitalized with TBI and survived was 99 per 100,000 population (260,000 cases). Hospitalization incidence patterns mirrored mortality rate patterns -- the highest rates were among persons 15-24 years of age and persons over age 65. Based on preliminary data from the Colorado TBI Registry and Follow-up System,25,26 we can estimate that each year, approximately 35 percent (80,500) of the 230,000 hospitalized survivors of TBI experience the onset of long-term disability. A small but unknown proportion of the more than 1 million persons with TBI who are not hospitalized may also experience long-term disability. If we assume this proportion is only 1 percent (existing data indicate it is probably greater), an additional 10,000 persons might have long-term disability. Thus, the estimated number of persons who become disabled each year from TBI is between 80,000 and 90,000.

Executive Summary
Introduction
CDC's Traumatic Brain Injury Surveillance Program, 1989-1998
Current Data on Traumatic Brain Injury Mortality and Morbidity
CDC Estimates of Traumatic Brain Injury-Related Disability
Public Health Goals
References
Appendix: Methods Used to Produce Estimates for This Report