About 1 in 7, or 13.5 percent of adults who encountered intense dust clouds after the collapse of the World Trade Center on September 11 were later found to have asthma, compared with just 8.4 percent who had no dust cloud exposure, researchers in Atlanta and New York City reported on Tuesday.

Likewise, among various groups of people connected to the Twin Tower collapse, rescue and recovery workers were more likely to have a diagnosis of asthma (12.2 percent) than passers-by (8.4 percent).

The results are from a survey, conducted from November 2006 through December 2007, to assess the health status of more than 46,000 adults five to six years after the disaster. 

That such a horrific event left lasting physical and emotional scars is, perhaps, no great surprise. Among adults with no prior diagnosis of post-traumatic stress disorder (PTSD), 23.8 percent have reported symptoms after September 11, and the prevalence of symptoms has increased over time, researchers reported in the Journal of the American Medical Association.

The mental health effects, which can be debilitating and often chronic, "seem to be the largest health problem coming out of 9/11" says Lorna Thorpe, Ph.D., the deputy commissioner of the New York City Department of Health and Mental Hygiene Division of Epidemiology and one of the coauthors of the study. "But immediately after the 9/11 event, I don't think there was a clear understanding of what the physical impacts would be." 

People in the vicinity of the collapse had "the potential to inhale huge amounts of particulate matter," observes Joan Reibman, M.D., an associate professor of medicine and environmental medicine at the New York University School of Medicine and the director of the school's Bellevue Asthma Center, who was not involved in the study. "We think that could act as a real irritant to the airways."

Some 23 million Americans have asthma, a lung condition that causes airway swelling and inflammation. People with asthma may experience repeated bouts of coughing, wheezing, shortness of breath, and tightness in the chest.