Injury death rates nationally rose 5.5 percent after a two-decade period of decline, according to a study released last month by the Centers for Disease Control and Prevention (CDC). The largest increases were seen in the 20-29 and 45-54 year age groups, the study indicated.

The total injury mortality rate includes deaths from unintentional injury, suicides, homicides and injuries of undetermined intent. Homicide rates remained stable throughout the 1999-2004 period, with unintentional poisonings accounting for more than half of the total increase in injury deaths.

The 45-54 year-old age group experienced the largest increase in injury mortality rates: a 25 percent increase, for an additional 8,000 deaths in 2004. In comparison, the 20-29 year age group had an 8 percent increase in total injury death rates. Unintentional poisonings accounted for more than 50 percent of the increase in each group.

Shared risk factors could contribute to the increase in multiple injury categories and age groups, according to CDC. For example, the recent increase in prescription drug abuse during the same time period in these age groups could have contributed to an increase in mortality due to suicide, homicide, unintentional poisoning, and other types of unintentional injury. Prevention programs that focus on such shared risk factors could help reduce the number of injury-related deaths.

For this study, CDC analyzed mortality data on resident deaths occurring in the United States, as compiled from death certificates by the National Vital Statistics System.