Seven years after the terrorist attacks on the New York’s Twin Tours the health of hundreds of Americans witnessing the disastrous scene or having to do with people injured in the crash is still showing signs of deterioration.

According to a new study released Wednesday from the World Trade Center Health Registry, most of these people seem to suffer from asthma, posttraumatic stress disorder or psychological distress. The good news is that people can receive free treatment, as the city offers free physical and mental health care to eligible people affected by the attacks.

“The health impact of 9/11 reached far beyond the deaths and injuries that occurred that day. But many of the health issues that have emerged, such as asthma and [posttraumatic stress disorder], are treatable. Free treatment is available. Anyone still in need of help should call 311 or visit nyc.gov,” Lorna Thorpe, the Health Department's deputy commissioner for epidemiology, said.

According to background information of the study, more than 400,000 people were heavily exposed to the disaster. They all agreed to be tracked for up to 20 years after 2001. More than half of them reported being in the dust cloud from the collapsing towers; 70 percent witnessed a traumatic sight, such as a plane hitting the tower or falling bodies; and 13 percent sustained an injury that day. Of them, 25,000 to 70,000 people developed posttraumatic stress disorder and 3,800 to 12,600 people may have developed asthma.

However, the study focused on 71,437 people registered in the World Trade Center Health Registry. They included rescue and recovery workers, Lower Manhattan residents, are workers, commuters and passerby. The study found that two to three years after the attacks, 3 percent of adults reported they had developed new asthma, 16 percent likely had posttraumatic stress disorder and 8 percent had severe psychological distress. The rate of new asthma was highest -- 6 percent -- among rescue and recovery workers who worked on the debris pile at Ground Zero. Those injured, with low income and Hispanics had the highest rate of posttraumatic stress disorder. Generally, minorities and low-income respondents experienced higher rates of mental and physical problems, as did women.

“The consensus among physicians is that when it comes to physical health, not everybody felt symptoms right away, though the vast majority felt them the first year. Some people developed symptoms years later. And in some cases, it's hard to tell whether they're World Trade Center-related or a result of allergies or existing conditions,” said Lorna Thorpe, the deputy commissioner for epidemiology at the New York City Health Department.

The study, conducted by the Health Department and the federal Centers for Disease Control’s Agency for Toxic Substances and Disease Registry, was published in the Journal of Urban Health.