The effect of counting principal and secondary injuries on national estimates of motor vehicle-related trauma: a NEISS-AIP special study.

OBJECTIVE To demonstrate the effect of including both principal and secondary injuries in the calculation of national estimates of non-fatal motor vehicle-related injury, using the National Electronic Injury Surveillance System-All Injury Program (NEISS-AIP). METHODS The setting was a stratified sample of 15 US hospital emergency departments selected among 50 NEISS-AIP hospitals which agreed to participate in the study. Non-fatal injury data from a special study of the 2004 NEISS-AIP were analysed which allowed up to five injuries to be coded per case. National estimates of number and rate of injuries for 2004 were calculated, first using principal injuries alone, then by including principal and secondary injuries. RESULTS An estimated 4,833,626 principal and secondary injuries were sustained by the estimated 2,893,782 motor vehicle occupants involved in a crash and treated in US hospital emergency departments (EDs) in 2004. This represents a 67% increase in the total number of injuries compared with an estimate of principal injury alone. Incidence of contusions/abrasions and lower trunk injuries rose most steeply among broad injury types, and whiplash injury rose 18% in number and rate. A significantly lower percentage of cases with a single listed injury were hospitalised (5%) compared with those who sustained multiple injuries (8%). CONCLUSIONS Based on an analysis of NEISS-AIP special study data, the inclusion of both principal and secondary injuries in national estimates of motor vehicle-related occupant injury would provide a more comprehensive report of non-fatal injuries treated in US hospital EDs. Other countries with ED-based surveillance systems could consider reporting multiple injuries when assessing injury count associated with motor vehicle trauma requiring ED care.