Story highlights 5,441 people have enrolled in the World Trade Center Health Program

They have been diagnosed with 6,378 separate cancers

(CNN) Next month will mark 15 years since the terrorist attacks of September 11, 2001, but thousands of people across the country continue to feel its effects on their health.

As of June 30, the Centers for Disease Control and Prevention's World Trade Center Health Program enrolled more than 5,400 people who have been diagnosed with cancers linked to the 9/11 attacks, according to statistics released by the program. That's triple the number of people enrolled with cancer diagnoses since January 2014, when 1,822 had signed up.

From January 2013 to January 2016, the number steadily increased by an average of 1,525 people per year. The number of people with 9/11-related cancers could be even higher; the 5,441 number reflects only the people who've chosen to enroll in the federal health program. The program provides health care, medical monitoring and treatment to thousands of people directly affected by the 9/11 attacks.

"We continue to do outreach efforts to see who is eligible and out there," said Christy Spring, public affairs specialist for the CDC's National Institute for Occupational Safety and Health.

Among those in the program, 4,692 are first responders, emergency responders, recovery and cleanup workers, and volunteers who helped in the aftermath of the attacks on the World Trade Center, the Pentagon and the crash site near Shanksville, Pennsylvania. The other 749 people are other survivors who lived, worked or went to school near the World Trade Center on September 11 or in the subsequent months. Almost half of the 5,441 with cancer diagnoses range from ages 55 to 64.

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