(CNN) -- Nineteen former patients at a Denver, Colorado, hospital have tested positive for hepatitis C, federal prosecutors said Thursday as they announced new charges against a former hospital employee accused of exposing the patients to the virus.



A hospital worker is accused of injecting herself and using unclean syringes for patients.



Prosecutors charged Kristen Diane Parker with 21 counts of tampering with a consumer product and another 21 counts of obtaining a controlled substance by deceit or subterfuge, according to an indictment. Parker, 26, had previously faced three federal counts from earlier this month.



Parker, who worked as a surgical technician at Rose Medical Center in Denver, is accused of injecting herself with syringes that held patients' pain medication Fentanyl, then replacing the pain medication in the syringes with saline, according to a statement from the office of the U.S. attorney for Colorado.



In a statement to police during the investigation, Parker said, "I can't take back what I did, but I will have to live with it for the rest of my life, and so does everyone else."



Parker's attorney did not return a call from CNN on Thursday.



Authorities said Parker knew she had hepatitis C, a contagious liver disease. Hepatitis C can lead to cirrhosis or liver cancer, according to the Centers for Disease Control and Prevention.



Parker believes she contracted the virus through using heroin and sharing needles with other users while she lived in New Jersey in 2008, authorities said.



According to an affidavit filed by an investigator with the Food and Drug Administration, Rose Medical Center knew Parker tested positive for hepatitis C. She was counseled on how to limit her exposure to patients.



Parker worked at Rose Medical Center from October 2008 to April 2009, said Jeff Dorschner, a spokesman for the U.S. attorney for Colorado.



Parker's employment was terminated after she failed a hospital-ordered drug test, said Leslie Teegarden, spokeswoman for Rose Medical Center. The tests were ordered after co-workers reported "suspicious behavior,"  Teegarden said Thursday.



Rose Medical Center contacted about 4,700 patients who may have been exposed to the virus, according to a statement on the center's Web site. Of those patients, 3,540 have been tested thus far, Teegarden said. She said the hospital plans to use tamper-resistant, pre-filled Fentanyl syringes to prevent intentional contaminations.



Parker also worked at Northern Westchester Hospital in New York and Audubon Ambulatory Surgical Center in Colorado Springs, Colorado. Prosecutors have not charged her with any crimes related to her employment at the other two facilities.



About 1,200 patients may have been exposed between May 4 and July 1 of this year, when Parker worked at Audubon, according to the center's Web site.



As of last week, 545 of Audobon's former patients had been tested for the virus, according to the Colorado Department of Public Health and Environment. One patient tested positive for hepatitis C, but that infection could not be linked to Parker, according to the department's Web site. Nearly 1,000 patients had been tested as of Thursday, said Audubon spokeswoman Amy Triandiflou.



Details about what Parker may have done to expose Audubon patients to the virus are still sketchy, Triandiflou said.



More than 2,700 patients could have been exposed at Northern Westchester Hospital, according to the hospital's Web site. The site did not indicate whether any infections had been detected.



There is no vaccine for hepatitis C.



If Parker is convicted and if any one of the former patients suffers serious bodily injury because of her actions, she could face a maximum of 20 years in federal prison, prosecutors said. If she is convicted and if any one of the former patients dies as a result of the infection, she could be sentenced to life in prison, according to prosecutors.



CNN's Jim Spellman contributed to this report.
How many former patients tested positive? What is Parker accused of? Where does Parker work? how many former patients twho asested positive? who was accused of using syringes filled with pain medication? what city was hospital worker living in?
Nineteen 21 counts of tampering with a consumer product and another 21 counts of obtaining a controlled substance by deceit or subterfuge, Rose Medical Center Nineteen Kristen Diane Parker Denver, Colorado,
question: How many former patients tested positive?, answer: Nineteen | question: What is Parker accused of?, answer: 21 counts of tampering with a consumer product and another 21 counts of obtaining a controlled substance by deceit or subterfuge, | question: Where does Parker work?, answer: Rose Medical Center | question: how many former patients twho asested positive?, answer: Nineteen | question: who was accused of using syringes filled with pain medication?, answer: Kristen Diane Parker | question: what city was hospital worker living in?, answer: Denver, Colorado,