NEW YORK (Reuters Life!) - Many civilian survivors of the September 11 attacks on the World Trade Center were still suffering from symptoms of post-traumatic stress several years after the 2001 disaster, according to a study.
The study, the first to focus on the long-term mental health of people who were actually in the Twin Towers on the morning of September 11, also found that the biggest predictor of long-term post-traumatic stress disorder (PTSD) had nothing to do with the disaster itself.
Instead, it was income.
The research team, led by Sandro Galea of Columbia University in New York, surveyed nearly 3,700 people who escaped the Trade Center and found that 96 percent still had at least one symptom of PTSD two to three years later.
Of those, 15 percent screened positive for full-blown PTSD, a rate about four times higher than that seen in the general population in any given year.
"We are learning that (September11) had pernicious and long-lasting mental health effects," Galea said of the study, reported in the American Journal of Epidemiology.
Past studies have looked at the general public, or people who lived near the World Trade Center, rather than those who were actually in it.
That's because researchers at first had no good way of finding and studying survivors who had escaped the buildings that day. But government officials have since developed a health registry that includes a large sample of people who were in the Trade Center.
Galea said his team's findings help pinpoint survivors who appear to be at particular risk of long-term PTSD. Not surprisingly, the risk rose along with the severity of the trauma people went through on September 11.
People who had escaped from floors above the planes' "impact zone" were at greater risk than those who had escaped from lower floors. Similarly, people who were evacuated relatively later, or who had to run from the cloud of debris sent out by the collapsing towers, were also at elevated risk.
In addition, survivors who were injured or personally witnessed a "horror," such as people falling or jumping from the towers, were at increased risk.
Of those who said they witnessed a horror, 16 percent had probable PTSD two to three years later, against 4 percent of those without such experiences.
Galea said the findings had implications for disaster planning, noting that those who did not start evacuating after the first plane hit were at relatively greater risk of PTSD.
"This tells us, for example, that any delay in evacuation matters. This also tells us that you want to get people clear of the area quickly, so that they don't have to witness any more bad things," he added.
But his team found that the biggest predictor of long-term PTSD was income.
Among the lowest income survivors, those making less than $25,000 at the time of the study, half had probable PTSD. That compared with 6 percent of survivors earning at least $100,000.
"There could be many explanations, but one is access to resources," Galea said, referring to the fact that higher income people have more options for getting support.
In addition, lower income people may already have had more stress in their lives before the attacks, and the trauma may have compounded existing problems, Galea said.
Reporting by Amy Norton at Reuters Health; editing by Elaine Lies