New York City's chief medical examiner, Dr Charles S Hirsch, has for the first time directly linked her death to exposure to dust from the destruction of the World Trade Center. In a letter made public on Wednesday, Hirsch said that he was certain "beyond a reasonable doubt" that dust from the twin towers contributed to the death of Felicia Dunn-Jones.

Hirsch said he had decided to amend Dunn-Jones' death certificate to indicate that exposure to trade center dust "was contributory to her death". The manner of death will be changed from natural causes to homicide. Her name will be added to the official list of World Trade Center victims, and the official number of people who died as a result of the attack on the twin towers will be increased to 2,750.

By making a formal connection between Dunn-Jones' death and her relatively brief exposure to the dust, the medical examiner's decision could have a wide impact on how the city deals with the growing number of illnesses and deaths linked in some way to ground zero.

The city is already under pressure to re-examine the deaths of people like James Zadroga, 34, a New York police detective who worked at the debris pile in the months after the towers fell. Although a New Jersey pathologist's autopsy last year concluded that his death was linked to trade center dust, city officials have not accepted that.

"The city medical examiner has now accepted what thousands of people with 9/11-related illnesses and their doctors have long understood: that ground zero dust was harmful and even deadly," said Rep Carolyn B Maloney. She and Rep Vito J Fossella, both of New York, had appealed to Hirsch to change his original decision on Dunn-Jones.

Maloney urged Hirsch on Wednesday to review other cases of people who died after being exposed to the dust. The medical examiner's office said it had no plans to undertake such a review.

But the New York State Department of Health, with financial assistance from the National Institute for Occupational Safety and Health, has started to study deaths among those who responded to the disaster.

The medical examiner's decision also could be cited as supporting evidence in the federal lawsuits filed against the city by thousands of firefighters, police officers and recovery workers who say they were injured by breathing the dust during the 10-month cleanup.

"This will bring us some closure, but hopefully it will also open doors for others to get the medical compensation they need," Joseph Jones, Dunn-Jones' husband, said in a telephone interview.

Dunn-Jones' death is now considered a homicide and raises the trade center death toll to 2,750.