The effect of a terrorist attack on emergency department inflow: an observation study using difference-in-differences methodology

STUDY OBJECTIVE: The objective of this study was to investigate how the terrorist attack in Stockholm, Sweden affected patient inflow to the general emergency departments (EDs) in close proximity of the attack. The study analyzed if, and to what extent, the attack impacted ED inflow during the following days and weeks. METHODS: In a retrospective observational study, anonymized aggregated data on ED arrivals (inflow of patients) to all seven of the EDs in the Stockholm County was analyzed using the Difference-in-Differences (DiD) estimator. The control groups were the affected hospitals in the years prior to the terrorist attack. The number of ED visits was retrieved from the Stockholm County Council administrative database. RESULTS: The study shows a statistically significant reduction in overall ED inflow of 7–9% following the attack. The effect was strongest initially after the attack, and ED inflow regained normal levels within approximately three weeks’ time, without any significant rebound effect. The effect on ED inflow also decreased with distance from ground zero, and was not significant further away than 10 km. CONCLUSION: The results showed that ED inflow was significantly decreased in the weeks immediately following the Stockholm terrorist attack. The reasons for this cannot be fully explained in this observational study. However, the results suggest that some patients actively choose when, where and if they should go to the ED.