A longitudinal analysis of PTSD symptom course: delayed-onset PTSD in Somalia peacekeepers.

Posttraumatic stress disorder (PTSD) typically follows an acute to chronic course. However, some trauma victims do not report significant symptoms until a period of time has elapsed after the event. Although originally dismissed as an artifact of retrospective methodologies, recent prospective studies document apparent instances of delayed-onset PTSD. Little is known currently about factors associated with the delayed onset of PTSD. This study was designed to examine the course of PTSD in a sample of 1,040 U.S. military peacekeepers who served in Somalia. A small but nontrivial subset of participants endorsed clinically significant levels of PTSD after a period of minimal distress, the magnitude of which cannot be ascribed to minor waxing and waning of symptoms. War-zone exposure and perceived meaningfulness of the mission, as rated by soldiers after returning to the United States, predicted symptom course over the next 18 months.