News Release

Researchers find high rates of mental disorders in Oklahoma City bombing survivors

Peer-Reviewed Publication

Washington University School of Medicine

St. Louis, Aug. 25, 1999-- In addition to the physical damage and devastation that it caused, the 1995 Oklahoma City bombing had a major impact on mental health. In a study of survivors, researchers from Washington University School of Medicine in St. Louis, the University of Oklahoma and the Oklahoma State Department of Health have found that almost half suffered from postdisaster psychiatric disorders in the months after the explosion. And they were able to identify the symptoms that indicated the need for treatment.

In the Aug. 25, 1999, issue of the Journal of the American Medical Association, the investigators report that 45 percent of the survivors surveyed had psychiatric problems in the six months following the bombing. Just over 34 percent had posttraumatic stress disorder (PTSD).

"This tragic event was extremely severe both in scope and intensity," said principal investigator Carol S. North, M.D., associate professor of psychiatry at Washington University School of Medicine. "Over the years, our group has studied survivors of 13 different disasters, and the 34 percent rate of posttraumatic stress disorder after the Oklahoma City bombing is the highest in any of the studies we've done to date."

Part of the reason may have been the magnitude of the disaster. The bombing of the Alfred P. Murrah Federal Building killed 167 people, including 19 children. Another 684 people were injured. More than 800 structures in the area were either demolished or damaged, and the estimated property loss was $625 million.

For this study, the investigators randomly selected 255 survivors from a confidential registry of 1,098 survivors maintained by the Oklahoma State Department of Health. Some were unreachable, and others refused to be interviewed, so 182 eventually were surveyed, using a structured interview called the Diagnostic Interview Schedule/Disaster Supplement, which assesses the mental health of disaster survivors and their disaster experience. The Disaster Supplement was developed by Washington University psychiatric epidemiolgists Lee N. Robins, Ph.D., and the late Elizabeth M. Smith, Ph.D. It was further revised and developed by Smith and North to assess the mental health of disaster survivors.

Of the survivors interviewed, 87 percent were injured in some way by the blast, and 82 percent saw someone injured or killed. Almost half (46 percent) reported thinking they were going to die at the time of the explosion, and 43 percent lost a family member or friend. Of the 182 survivors surveyed, 92 percent knew someone who was injured or killed in the bombing. The survivors were interviewed an average of six months after the bombing.

Posttraumatic stress disorder is the classic psychiatric disorder seen in disaster survivors, and some symptoms occur in just about everyone, but an official diagnosis of PTSD requires several things.

First, a person must be exposed to a life event that threatens life or limb: an accident, an explosion, combat or some other threatening circumstance. After exposure to such an event, mental health professionals look for three groups of symptoms that comprise PTSD.

The first group involves intrusive reexperience symptoms-- these include flashbacks and nightmares about the event. Another group involves hyperarousal symptoms, including feeling jumpy, having trouble sleeping or concentrating, and being startled easily. The remaining set involves avoidance and numbing symptoms. They include not wanting to think about an event, feeling distant, feeling numb or isolated from people and wanting to avoid reminders of an event. For an official diagnosis of PTSD, those symptoms must linger for at least a month and cause distress or problems in daily life.

Just over a third of the survivors in this study met the official definition of PTSD, but the experience of some posttraumatic stress symptoms was nearly universal. Almost all survivors had flashbacks, nightmares or other intrusive reexperience symptoms. Hyperarousal symptoms also were common.

The least common PTSD symptoms also were the best predictors of the disorder. Survivors with at least three avoidance and numbing symptoms had an eventual diagnosis of PTSD 94 percent of the time.

"Therefore we recommend that disaster intervention workers be alert for avoidance and numbing symptoms because they are most predictive of posttraumatic stress disorder, for which referral for psychiatric evaluation is needed," North said. "The rest tend to be distressed and hyperaroused and to have intrusive reexperience, but this doesn't mean that they're psychiatrically ill. Those symptoms may represent a normal or understandable response to abnormal events."

Those with avoidance and numbing symptoms also were more likely to have other psychiatric problems. For example, 55 percent of those with PTSD also were diagnosed as clinically depressed. Those with PTSD and another disorder were the most likely to be functionally impaired and to have problems with relationships and problems performing their work.

"Because of this, we also recommend that mental health professionals don't stop searching for disorders once they find PTSD. There may be a comorbid disorder that signifies a much more serious disturbance that will need more serious medical attention," North said.

The symptoms of PTSD begin in a hurry, the study found, because 76 percent of the subjects with the disorder reported onset of symptoms the same day as the event, and 94 percent had developed symptoms by the end of the first week. Factors that increased the risk of PTSD included pre-existing psychiatric conditions. And those who were more seriously injured were at greater risk, as were those who reported injury or death of a family member or friend.

Over the years, Smith, North and colleagues have done extensive research with survivors of natural disasters. They have studied earthquakes and floods, industrial and technological accidents such as plane crashes, and man-made disasters such as the terrorist bombing in Oklahoma City and a cafeteria mass shooting in Killeen, Texas. The 34 percent rate of PTSD after the bombing compares with a rate of 2 percent after a tornado, 28 percent after the mass shooting and 29 percent after a plane crashed into a hotel.

A unique funding arrangement with the National Institute of Mental Health allowed the investigators to get into the field as early as a month after a disaster, making it possible to compare disasters with one another and learn more about standard responses to unnatural events.

"Generally, disasters caused by willful human action are thought to do the most harm to mental well-being. Technological accidents which involve the human element but are accidental rather than willful, may be slightly less severe but still more severe than natural disasters or 'acts of God' like tornadoes. But as we develop a systematic database, we should be able to see if these theories hold," North said.

Although North thinks that the scope of the Oklahoma City bombing makes it difficult to compare with other disasters, she believes some important implications emerge from this study. First, because virtually all the cases of PTSD started almost right away, it is possible to begin to identify survivors with PTSD almost immediately. In addition, since most people who developed any psychiatric disorder also developed PTSD, concentrating on diagnosis of PTSD could identify those most likely to need psychiatric care.

The study also found that without avoidance and numbing, the nearly universal PTSD symptoms of intrusive reexperience and hyperarousal were not necessarily associated with later serious problems. Although survivors with those symptoms may benefit from reassurance and support, most will not require psychiatric intervention.

"There are two things for mental health providers to think about after a disaster, and our data on the Oklahoma City bombing reaffirm this" North said. "One is that some people become psychiatrically ill, but the other is that the majority of people do not. Most of them may have unpleasant symptoms and feelings and experiences, but that doesn't mean that they're ill."

North and colleagues now are analyzing follow-up data to learn whether PTSD and other illnesses persisted in survivors of the Oklahoma City bombing. They also want to learn whether any new illness developed more than six months after the event.


This research was supported by a grant from the National Institute of Mental Health.

North CS, et al. The Psychiatric Impact of the Oklahoma City Bombing on Survivors of the Direct Blast. Journal of the American Medical Association, vol. 282 (8) pp 755-762, Aug. 25, 1999.

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