New onset and persistent symptoms of post-traumatic stress disorder self reported after deployment and combat exposures: prospective population based US military cohort study.

OBJECTIVE: To describe new onset and persistence of self reported post-traumatic stress disorder symptoms in a large population based military cohort, many of whom were deployed in support of the wars in Iraq and Afghanistan.
DESIGN: Prospective cohort analysis. SETTING AND PARTICIPANTS: Survey enrolment data from the millennium cohort (July 2001 to June 2003) obtained before the wars in Iraq and Afghanistan. Follow-up (June 2004 to February 2006) data on health outcomes collected from 50 184 participants. MAIN OUTCOME MEASURES: Self reported post-traumatic stress disorder as measured by the posttraumatic stress disorder checklist-civilian version using Diagnostic and Statistical Manual of Mental Disorders, fourth edition criteria.
RESULTS: More than 40% of the cohort were deployed between 2001 and 2006; between baseline and follow-up, 24% deployed for the first time in support of the wars in Iraq and Afghanistan. New incidence rates of 10-13 cases of post-traumatic stress disorder per 1000 person years occurred in the millennium cohort. New onset self reported post-traumatic stress disorder symptoms or diagnosis were identified in 7.6-8.7% of deployers who reported combat exposures, 1.4-2.1% of deployers who did not report combat exposures, and 2.3-3.0% of non-deployers. Among those with self reported symptoms of post-traumatic stress disorder at baseline, deployment did not affect persistence of symptoms.
CONCLUSIONS: After adjustment for baseline characteristics, these prospective data indicate a threefold increase in new onset self reported post-traumatic stress disorder symptoms or diagnosis among deployed military personnel who reported combat exposures. The findings define the importance of post-traumatic stress disorder in this population and emphasise that specific combat exposures, rather than deployment itself, significantly affect the onset of symptoms of post-traumatic stress disorder after deployment.