In addition, approximately 10-to-20 percent of rescue workers and 5-to-10 percent of the general population may experience PTSD symptoms, including flashbacks, recurrent dreams of the event, survival guilt and hyper-vigilance.
"Our review of studies conducted in the aftermath of disasters during the past 40 years shows that there is a substantial burden of PTSD among people who experience a disaster," said Sandro Galea, lead author of an article on the topic appearing in the current issue of Epidemiologic Reviews.
"Our analysis also shows that the most important risk factors for the development of PTSD are the extent of exposure to the disaster and the scope of the disaster."
Funded in part by the National Institutes of Health, the study considered the evidence from peer-reviewed studies conducted between 1980, when PTSD was first included as a disorder in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, and 2003.
The earliest disaster included in the review was a 1963 landslide and flood that took place in northeastern Italy. The most recent was the September 11 terrorist attack in New York City.
Although the prevalence of PTSD has previously been found to be higher after human-made and technological disasters than after natural disasters, Galea notes that this difference is largely due to differences in sampling.
"Most studies conducted after human-made and technological disasters have focused on direct victims, while studies of natural disasters typically include samples of people in the overall community who probably had substantially lower exposure to the disaster," he said.
In addition to exposure to a disaster, a number of other risk factors for PTSD were found to be important across multiple studies.
Women consistently have a higher prevalence of PTSID after disasters than men, as do persons with pre-existing or concurrent psychiatric disorders and those who have previously experienced traumatic events or substantial stress.
Galea, an M.D. who is an associate professor at the U-M School of Public Health and a research affiliate at the U-M Institute for Social Research, is involved in several other ongoing research projects related to the mental health consequences of disasters.
One is a study of mental health service use among uniformed service providers in New York City in the first five years after the September 11 attacks. Another is a study of how social context, including income inequality, influences an individual's underlying strengths and vulnerabilities in the aftermath of a disaster.
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