Whereas most people who go through traumatic events experience a brief acute response to the stressful situation and never develop an enduring pathologic reaction, a smaller proportion of people will develop PTSD, either alone or complicated with comorbid disorders such as depression, generalized anxiety disorder, or substance misuse.[27]Neria Y, Gross R, Olfson M, et al. Posttraumatic stress disorder in primary care one year after the 9/11 attacks. Gen Hosp Psychiatry. 2006 May-Jun;28(3):213-22.
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[30]Kessler RC, Sonnega A, Bromet E, et al. Posttraumatic stress disorder in the National Comorbidity Survey. Arch Gen Psychiatry. 1995 Dec;52(12):1048-60.
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[118]Shalev AY, Freedman S, Peri T, et al. Prospective study of posttraumatic stress disorder and depression following trauma. Am J Psychiatry. 1998 May;155(5):630-7.
http://www.ncbi.nlm.nih.gov/pubmed/9585714?tool=bestpractice.com
The transition from acute to long term, and the disease course, are varied and influenced by risk and protective factors. For example, availability of treatment, social support, and effective coping strategies might influence recovery. Severity of exposure and loss of life and property might be associated with a long and complicated course of illness.[119]Galea S, Ahern J, Resnick H, et al. Psychological sequelae of the September 11 terrorist attacks in New York City. N Engl J Med. 2002 Mar 28;346(13):982-7.
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http://www.ncbi.nlm.nih.gov/pubmed/11919308?tool=bestpractice.com
The average duration of symptoms, if treated, is 36 months, and the average duration of symptoms among those untreated is 64 months. Moreover, while almost 50% experience significant reduction in symptoms, more than one third of people never fully remit.[30]Kessler RC, Sonnega A, Bromet E, et al. Posttraumatic stress disorder in the National Comorbidity Survey. Arch Gen Psychiatry. 1995 Dec;52(12):1048-60.
http://www.ncbi.nlm.nih.gov/pubmed/7492257?tool=bestpractice.com