( 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 ca n'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 .
Denver , Colorado , social worker accused of exposing patients to hepatitis C. Two former patients test positive for hepatitis C , which affects the liver . Kristen Diane was accused of using syringes filled with pain killers Fentanyl . Police say she refilled syringes meant for patients with saline solution .