Hospitalizations for injury in New Zealand: prior injury as a risk factor for assaultive injury.

OBJECTIVES This study sought to determine the degree to which injury hospitalization, especially for assaultive injury, is a risk for subsequent hospitalization due to assault. METHODS A New Zealand hospitalization database was used to perform a retrospective cohort study. Exposure was defined as an injury hospitalization, stratified into assaultive and nonassaultive mechanisms. Hospitalizations for an assault during a 12-month follow-up period were measured. RESULTS Individuals with a prior nonassaultive injury were 3.2 times more likely to be admitted for an assault than those with no injury admission (95% confidence interval [CI] = 2.7, 3.9). The relative risk associated with a prior assault was 39.5 (95% CI = 35.8, 43.5), and the subsequent admission rate did not vary significantly by sex, race, or marital or employment status. Among those readmitted for an assault, 70% were readmitted within 30 days of the initial hospitalization. CONCLUSIONS Prior injury is a risk for serious assault, and the risk is even greater if the injury is due to assault. Risk of readmission for assault is largely independent of demographic factors and greatest within 30 days of the initial assault.