Objective.

To determine whether the risk of unintentional injury requiring emergency department (ED) or inpatient care in children is transiently increased over a 90-day period after injury to a sibling.

Design.

Retrospective cohort.

Setting.

King County, Washington.

Participants.

A total of 41 242 children 0 to 15 years of age continuously enrolled in Medicaid and living in King County during the period October 1, 1992 through September 30, 1993 (27 450 child-years).

Outcome Measures.

The outcome was an unintentional injury treated in the ED or inpatient setting. Incidence rates and hazard ratios were calculated for children whose sibling had been injured in the previous 90 days, compared with children without such exposure. Multivariate analysis was used to adjust for age, gender, race, sibling group size, and noninjury ED use.

Results.

There were 4921 injuries treated only in the ED and 82 hospital admissions. The incidence of ED treated injury was 305 per 1000 child-years among children whose sibling had been injured in the previous 90 days and 174 per 1000 child-years among children without this exposure (relative risk: 1.75; 95% confidence interval: 1.56–1.95). The incidence of injury-related hospitalization was 1.7 per 1000 child-years among children whose sibling had been injured in the previous 90 days, compared with 3.0 per 1000 child-years among children without this exposure (relative risk: .57; 95% confidence interval: .07–2.12). Injury risk peaked in the period 4 to 10 days after a sibling's injury and returned toward, but did not attain, baseline risk over the subsequent 2½ months. The magnitude of this effect depended on the child's age; the relative risk of injury was higher among older children.

Conclusions.

Injuries treated in the ED or inpatient setting appear to cluster within sibling groups over brief periods of time. Shared social or environmental exposures may contribute to this clustering and may be amenable to targeted, time-limited prevention interventions.

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