Syncope, active and reserve components, U.S. Armed Forces, 1998-2012.

During the period of 1 January 1998 to 31 December 2012, the health care records of 153,172 active component service members documented at least one health care encounter with a diagnosis of "syncope and collapse" (overall incidence rate of 7.2 cases per 1,000 person-years). The annual incidence rates rose by 89 percent during the period. During the 15-year surveillance period, there were 4,954 instances of a documented health care encounter with a diagnosis of syncope on the same day that the service member had received an immunization by injection. Annual rates of syncope associated with immunization ranged from a low of 4.4 events per 100,000 immunization episodes in 1998 to a maximum of 14.1 events per 100,000 episodes in 2006. For both syncope diagnoses in general and syncope associated with immunization, rates were higher among women than men and were highest among those under age 20. Nearly ten percent of syncopal events associated with immunization occurred during the first two weeks of military service. Rates of syncope increased with the number of injections received per immunization episode. Diagnoses of physical injury were documented in the records of health care encounters for syncope for 4.0 percent of all syncopal events and 6.9 percent of episodes of syncope linked to immunizations.