Increases in Age-Group--Specific Injury Mortality --- United States, 1999--2004

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From 1979 to 1999, total injury mortality rates* declined overall in the United States, despite increases in suicide rates in the late 1980s and in homicide rates in the early 1990s (CDC, unpublished data, 2007). From 1999 to 2004, however, total injury mortality rates increased 5.5%, from 53.3 to 56.2 per 100,000 population, the first sustained increase in 25 years. To assess this increase, CDC analyzed the most recent data from the National Vital Statistics System (NVSS). This report summarizes the results of that analysis, which determined that U.S. mortality rates increased from 1999 to 2004 for unintentional injuries, suicides, and injuries of undetermined intent; homicide rates were stable. Among persons aged 45--54 years, the total injury mortality rate increased 24.5%, including an 87.0% increase in the mortality rate from unintentional poisoning (most commonly drug poisoning) and a 48.0% increase in suicide by hanging/suffocation. Among persons aged 20--29 years, the total injury mortality rate increased 7.7%, including a 92.5% increase in the death rate from unintentional poisoning and a 31.7% increase in suicide by hanging/suffocation. Parallel increases in multiple categories and mechanisms of injuries within these two age groups suggest an increase in one or more shared risk factors (e.g., drug abuse); prevention programs that focus on shared risk factors might help reduce deaths from injuries.

Mortality data on deaths among residents in the United States were obtained from death certificate information recorded by NVSS and accessed via the CDC WISQARS online database.^† For this study, the total injury category included deaths from unintentional injury, suicide, homicide, injury of undetermined intent, legal intervention, and operations of war.^§ Rates were age-adjusted to the 2000 standard U.S. population using bridged-race^¶ population figures. Percentage changes from 1999 to 2004 in death rates by age group were calculated for the three most common injury categories, and correlations in age-group--specific changes among these categories were tested using Pearson correlation coefficients.

The analysis indicated that, overall in the United States, injury mortality increased 5.5% from 1999 to 2004. Unintentional injury mortality rates increased 6.6%, suicide increased 4.3%, and deaths from injury of undetermined intent increased 20.6%. Rates of homicide declined 2.0%, and rates of death by legal intervention declined 9.5% (Table 1). Increases in poisoning mortality accounted for 61.9% of the increase in unintentional injury, 28.0% of the increase in suicide, 81.2% of the increase in deaths from injury of undetermined intent, and 55.7% of the increase in total injury mortality.

The numbers of deaths by age group were sufficient to examine age-group--specific changes in death rates for the three most common injury categories: unintentional injury, suicide, and homicide. Increases in unintentional injury occurred among persons aged 20--64 years (Figure). Suicide increases occurred among persons aged 40--64 years. Homicide rates declined for all persons except those aged 25--34 and 45--54 years. For unintentional injury and homicide, rates declined for persons aged <20 years. For all three categories, rates generally declined for persons aged >65 years. The age-group--specific changes for suicide and homicide correlated in direction and magnitude with those for unintentional injury (r = 0.62, p = 0.01 for unintentional injury versus suicide; r = 0.86, p<0.001 for unintentional injury versus homicide). The correlation between suicide and homicide was not statistically significant (r = 0.42, p = 0.10).

Injury mechanisms were analyzed for the two age groups with the greatest percentage changes in injury mortality rates from 1999 to 2004: persons aged 20--29 years and persons aged 45--54 years (Figure). Among persons aged 20--29 years, the unintentional injury rate increased 12.1%, primarily the result of a 92.5% increase in the rate for poisoning deaths. The 1999 and 2004 suicide rates were similar for this age group; the rate for hanging/suffocation suicides increased 31.7%, but the rate for firearm suicides declined 13.2% (Table 2). In this age group, the increase in unintentional poisoning accounted for 54.0% of the 7.7% increase in the overall injury mortality rate.

Among persons aged 45--54 years, the unintentional injury rate increased 28.0% from 1999 to 2004, largely as the result of an 87.0% increase in the rate for poisoning deaths. The suicide rate increased 19.5% during the same period, largely as a result of increases of 23.7% in poisoning suicides and 48.0% in hanging/suffocation suicides (Table 2). In this age group, the increase in unintentional poisoning accounted for 51.6% of the 24.5% increase in the overall injury mortality rate.

Reported by: L Paulozzi, MD, Div of Unintentional Injury Prevention; A Crosby, MD, Div of Violence Prevention; G Ryan, PhD, Office of Statistics and Programming, National Center for Injury Prevention and Control, CDC.

Editorial Note:

The rate for unintentional injury deaths, the largest component of the total injury mortality rate, declined in the United States from 1979 until leveling in the late 1990s; the rate began to increase in 1999 (CDC, unpublished data, 2007). Findings in this report indicate the increase in the unintentional injury mortality rate since 1999 has been restricted to persons aged 20--64 years. From 1999 to 2004, the greatest increases in death rates for unintentional injury, suicide, and homicide have occurred among persons aged 20--29 and 45--54 years. The parallel changes in these age groups across injury categories and injury mechanisms might be related to changes in one or more shared risk factors.

Increases in poisoning deaths were a common factor in the increases in death rates from unintentional injury, injury of undetermined intent, and suicide. Approximately 95% of poisoning deaths that are unintentional or of undetermined intent and 75% of poisoning suicides are caused by drug poisoning (CDC, unpublished data, 2007). Therefore, the increases in poisoning rates determined by this study represent increases in drug poisoning. The increase in drug poisoning mortality likely is related to an increase in drug abuse, especially prescription drug abuse, since 1999 (1,2). During 2002--2005, the illicit use of drugs other than marijuana by persons aged 18--25 years increased from 7.9% to 8.8%. Illicit use of such drugs did not increase for all persons aged >26 years, but did increase among persons aged 50--59 years, from 2.7% to 4.4% (3).

The reason that substantial increases in hanging/suffocation suicides occurred in both of the age groups examined is uncertain. However, in addition to resulting in poisoning deaths, drug use can contribute indirectly to deaths through other mechanisms. Because drugs have pharmacologic effects (e.g., impairing coordination and removing inhibitions against risky or aggressive behavior), drug use might have contributed to the observed age-group--specific increases in nonpoisoning suicide, homicide, and unintentional deaths from falls, motor-vehicle traffic, fire/burns, and choking/suffocation. Furthermore, the cost of illicit drugs places an economic burden on drug abusers that contributes to risk for suicide or involvement in violent crime, and the system for distribution of illicit drugs promotes interpersonal violence and risk for homicide (4).

Epidemiologic evidence suggests that drug abuse has had measurable effects on rates of violence in the United States. Homicide rates among persons aged 20--29 years peaked during the crack cocaine poisoning epidemic of the late 1980s and early 1990s (CDC, unpublished data, 2007). Increasing suicide rates among adolescents from the 1970s through the early 1990s coincided with their increased exposure to alcohol and other drugs (5). Both drug users and nonusers living with drug users have higher rates of suicide and homicide (6). Drug users have rates of suicide and homicide 15--25 times those of the general population (7).

The findings in this report are subject to at least two limitations. First, death certificates do not record information regarding substance-abuse history or other risk factors (e.g., loss of social support or stressful life events) (8) that might have helped explain the increase in injury deaths from 1999 to 2004. Second, incorrect or incomplete information might result in misclassification of the intent of the deceased, especially when distinguishing between suicidal and unintentional drug poisoning.

Addressing the increase in total injury mortality in the United States will require concerted action by substance abuse, mental health, law enforcement, and public health agencies at local, state, and national levels. Integrated prevention programs that use various interventions (e.g., monitoring health behaviors, promoting help-seeking behavior, and enhancing availability of health and social support services), such as the U.S. Air Force suicide prevention program (9), might help reduce the number of deaths from unintentional injury, suicide, and homicide.

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