Prevalence and Course of Symptom-Defined PTSD in Individuals Directly or Indirectly Exposed to Terror: A Longitudinal Study.

OBJECTIVE: It is well established that direct exposure to terrorism can result in posttraumatic stress disorder (PTSD). However, individuals indirectly exposed to terrorism may also develop symptoms of PTSD. This study examined the prevalence and course of symptom-defined PTSD in employees who were present and not present at the site of a workplace terror attack.

METHODS: Survey data from ministerial employees were collected 10, 22, and 34 months after the 2011 bombing in the government district of Oslo. A total of 3,520 employees were initially invited to the study. Response rates of eligible participants were 56% (N = 1,974) at T1, 55% (N = 1,780) at T2, and 54% (N = 1,578) at T3. PTSD was measured using the Post-traumatic Stress Disorder Checklist-Specific (PCL-S). Symptom-defined PTSD was specified as meeting the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR), B, C, and D criteria.

RESULTS: Our findings showed a low and declining prevalence of symptom-defined PTSD in employees indirectly exposed to a workplace terror attack (4%, 3%, and 2% at the three respective times). In employees present at the site of the explosion, PTSD was six- to eightfold more prevalent (24%, 17%, and 17%).

CONCLUSIONS: Individuals indirectly exposed to terrorism may develop long-lasting posttraumatic stress reactions fulfilling PTSD symptom criteria. Due to the large number of individuals that may be indirectly exposed to terrorism, even a low risk of PTSD may result in high numbers of individuals with substantial posttraumatic stress. Our findings have implications for the planning and implementation of health care services beyond those directly exposed after large-scale terror events.