Previous Trauma Exposure and PTSD

This current study examined the influence of previous exposure to trauma on the risk of PTSD in a subsequent traumatic incident. The authors had multiple questions that they hoped to answer:

2,181 individuals from the general population were involved in the study. A 30-minute telephone interview assessed the different types of events, the number of times of occurrence, and the age of the participant at the time of trauma. The interview was in line with the criteria established in the DSM-IV for PTSD.

1,922 individuals had trauma after they were five years old. 17.5% experienced violent assault; 34% experienced another injury/shock, such as motor vehicle accident, disaster, life threatening disease etc.; 28.4% learned about a trauma that happened to a loved one; and 20% experienced a sudden, unexpected death of a loved one. Yet, of the 1,922 with these traumatic experiences, 38.6% had no previous exposure to trauma.

427 subjects were exposed to one event, 255 were exposed to two events, and 498 were exposed to three or more traumatic events. The study found that the risk of having PTSD was directly related to the number of traumatic exposures. Also, exposure to violent assault—no matter the number of times—largely increased a patient's predisposition to PTSD.

The rate of PTSD was twice as high for women than men.  But, in general, a patient's age during the interview and their current trauma was not related to risk. Also, the risk varied by the type of exposure. For example, violent assault (the highest) was ten times more likely to cause PTSD, than learning about a loved ones' trauma (the lowest).

In evaluating the effect of trauma over time, the authors found that the effects of violent assault exposure persisted over time with no changes. But for the other types of trauma and their after effects, the study found a decrease in influence of about 8% each year.

The authors stress the importance of a careful history when working with patients with PTSD, as childhood trauma seem to put patients at extra risk later in life:

"It should be noted that there is no evidence in these data that a trauma in childhood is associated with a higher risk of PTSD than is a trauma that occurred later in life; age at exposure to trauma was not found to be related to the risk of PTSD. We found, instead, that childhood trauma increased the risk that a new trauma experienced in adulthood would lead to PTSD."

In concluding the authors state that PTSD is a complex issue that cannot be simply isolated to one traumatic event in a patient's life. The sum total of all traumatic exposures must be examined to gain a better understanding of the situation.

"Specifically, our results show that respondents who experienced previous trauma are more vulnerable to the PTSD effects of subsequent trauma than those with no previous trauma. The results of this study also support the notions that repeated exposure to trauma has worse consequences than a single exposure and that the effects of previous assaultive violence are worse than the effects of previous trauma of lesser magnitude."

Breslau N, Chilcoat HD, Kessler RC, Davis GC. Previous exposure to trauma and PTSD effects of subsequent trauma: results from the Detroit area survey of trauma. American Journal of Psychiatry 1999;156:902-907.

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