Epidemiology of mass casualty incidents in the United States.

OBJECTIVE: We sought to characterize and estimate the frequency of mass casualty incidents (MCIs) occurring in the United States during the year 2010, as reported by emergency medical services (EMS) personnel.

METHODS: Using the 2010 National EMS Database of the National Emergency Medical Services Information System (NEMSIS), containing data from 32 states and territories, we estimated and weighted the frequency of MCIs documented by EMS personnel based on their perception of the event to produce incidence rates of MCIs per 100,000 population and MCIs per 1,000 9-1-1 calls requesting EMS service. We conducted descriptive analyses to characterize the MCIs by geographic location, incident type, and time of day as well as the MCI patients by demographic and health information. We used chi-squared tests to compare response delays and two-tailed t-tests to compare system response times between EMS responses documented as MCIs and those not.

RESULTS: Among the 9,776,094 EMS responses in the 2010 National EMS Database, 14,504 entries were documented as MCI. These entries represented an estimated 9,913 unique MCIs from the National EMS Database: 39.1% occurred in the South Atlantic region of the United States where only 19.1% of the population resides, 60.9% occurred in an urban setting, and 58.4% occurred on a street or highway. There were an estimated 13,677 MCI patients. The prehospital EMS personnel's primary impressions of the patients ranged from electrocution (0.01%) to traumatic injury (40.7%). Of the patients with a primary impression of injury (N = 7,960), motor vehicle traffic crash was the cause of injury for 62.7%. Among the MCI EMS responses, 47.6% documented experiencing a response delay compared to only 12.3% of non-MCI EMS responses.

CONCLUSIONS: This study demonstrates the range of health conditions and characteristics of EMS responses that EMS personnel perceive as MCIs, suggests that response delays are common during MCIs, and indicates there may be underreporting of all persons involved in an MCI. The National EMS Database is useful for describing MCIs and may help guide national leadership in strengthening EMS system preparedness for MCIs.