9/11 dust 'gave thousands asthma'

They included rescue and recovery workers, neighbouring office staff and passers-by.

A follow-up study of more than 46,000 people caught up in the terrorist attacks of September 11, 2001, found one in 10 had been diagnosed with asthma five or six years after the disaster. None of these 4,600 individuals had a previous history of the disease.

There was a strong association between exposure to the choking dust cloud generated by the collapse of the towers and asthma, the study found.

In total, 39pc of all those who developed asthma had been intensely exposed to the dust.

The most affected group was 21,600 rescue and recovery workers and volunteers, 12.2pc of whom became asthmatic.

More than 8pc of the next worst affected group - September 11 passers-by - suffered the disease.

The study's authors, led by Dr Robert Brackbill, from the Centres for Disease Control and Prevention in Atlanta, Georgia, wrote in the Journal of the American Medical Association (Jama): "These analyses confirm that intense dust cloud exposure was associated with new asthma diagnoses for each eligibility group, including the 1,913 passers-by who only had exposure to the area air and dust on September 11."

Among rescue and recovery workers, asthma risk was highest for those attending the scene of the attacks on September 11. Risk diminished for individuals who started work at later dates.

Asthma risk was also associated with damage to homes and offices. People who did not evacuate affected buildings had higher rates of asthma than those who did.

The same researchers found large numbers of people caught up in the attacks showed symptoms of post-traumatic stress disorder (PTSD).

Of 71,437 adults enrolled in the first part of the study conducted in 2003 and 2004, just over 14pc screened positive for symptoms probably caused by PTSD.

By the time 46,322 individuals were questioned for the follow-up study in 2006 and 2007, this proportion had risen to 19pc.

At follow-up, the prevalence of post-traumatic stress symptoms increased in every group studied, especially rescue and recovery workers. Passers-by were the most likely to be suffering symptoms (23.2pc) while neighbouring residents were the least (16.3pc).

Passers-by also had the highest prevalence of chronic PTSD symptoms.

Around 14pc of all participants previously free of PTSD were diagnosed with the disorder after September 11, and about the same percentage received a diagnosis of depression. More than 7pc of people had both diagnoses.

The occurrence of both asthma and PTSD symptoms was common among those taking part in the follow-up survey.

"Our findings confirm that, after a terrorist attack, mental health conditions can persist if not identified and adequately treated, and that a substantial number of exposed persons may develop late-onset symptoms," wrote the researchers. "Our study highlights the need for surveillance, outreach, treatment and evaluation of efforts for many years following a disaster to prevent and mitigate health consequences."