People who were heavily exposed to the Sept. 11 attacks on the World Trade Center had elevated risks of developing post-traumatic stress disorder symptoms even five years later, about four times that of the general public, according to a study released Tuesday.
The study by the city's Department of Health and Mental Hygiene found elevated levels of PTSD symptoms among the more than 46,000 people who were surveyed in 2006-2007. The study is based on data from a public health registry that tracks the health effects of Sept. 11.
Among survey respondents, 19 percent reported having symptoms, about four times the rate usually seen among adults. When the registry first surveyed people in 2003-2004, it was 14 percent.
Some in the first survey got better, while some remained where they were, and others got worse, said Lorna Thorpe, deputy commissioner for epidemiology and a co-author of the study.
"This is really the largest burden in terms of health conditions,'' Thorpe said.
The study found that more than half of the participants who reported having stress symptoms said they had not obtained treatment in the past year. The registry has begun outreach to get survey respondents referred for medical help, and the city offers free physical and mental health care to eligible people affected by the attacks.
Passers-by such as commuters and tourists were the most heavily affected, with 23 percent of them reporting symptoms in the latest survey.
The study contained better news about asthma. While those who developed respiratory symptoms soon after the attacks were still being diagnosed with asthma some years later, rates among people who first showed symptoms after 2003 were consistent with normal asthma rates.
"What this study shows fairly thoroughly, there was a very strong association between the intense exposure'' on Sept. 11 and the days immediately following, in terms of developing asthma, Thorpe said. "There were lingering effects, but those lingering effects have ameliorated.''
While asthma cases rose most sharply right after attacks, they were still being diagnosed after some years had passed. The study found that 10 percent of participants had been newly diagnosed with the condition between the attacks and the 2006-2007 survey period.
Rescue and recovery workers had the highest rates of new asthma diagnoses, and their risk was even higher if they were at the World Trade Center site on 9/11 itself or worked there for longer than 90 days. People who had to deal with heavy layers of dust in their homes or offices also had a higher risk of developing asthma.
The World Trade Center Health Registry was established in 2003 to track the long-term health effects of ground zero exposure on workers, volunteers, and residents. More than 71,000 people registered, and surveys on their health status was collected in 2003-2004 and 2006-2007. More than 46,000 registrants took part in both surveys.