Injury hospital discharge rates from 1988 to 2004: Do the trends vary by injury severity?

Rates of hospital discharges for injured persons ages 15-64 years decreased from 1988 to 2004. The objective of this research is to determine if trends in injury hospital discharge rates among those 15-64 years of age vary by injury severity. The National Hospital Discharge Survey (1988-2004) was used for the analysis. Survival Risk Ratios (SRR) were calculated by dividing the number of patients that survive a given ICD-9CM injury diagnosis code by the number of patients with that diagnosis code [(SRRs range from 0 (unsurvivable) to 1 (no threat to life)]. For discharges with multiple diagnoses, the diagnosis with the minimum SRR (i.e. lowest probability of survival) was used to determine severity. Injury discharge rates per 10,000 population were calculated using 7 different severity thresholds [discharges with a minimum SRR <=0.95 (most severe injuries only) to <=1.0 (all injuries)] by year for those ages 15-64 years. The trends for injury hospital discharge rates changed as the severity threshold changed. For example, the estimated rates for all injury discharges decreased on average 4% per year from 1988 to 2004, while rates calculated with discharges with a minimum SRR less than or equal to 0.995 (>=0.5% mortality) decreased on average 2% per year. The less rapid decline in rates of discharges for minor injuries could be explained by: 1) decreases in minor injury incidence due to prevention measures or 2) changes in health care delivery for minor injuries.