An investigation into the spread of the hepatitis C virus by a Colorado hospital worker has been expanded to two other states — New York and Texas — where the woman previously worked, the Associated Press reported.

According to Colorado officials, the woman, reportedly addicted to painkillers, took syringes filled with fentanyl, a powerful narcotic painkiller, from operating room carts and replaced them with used syringes filled with saline solution. The action is believed to have contaminated not only the swapped syringes but the containers of saline solution, the AP said.

Because of this, the AP said, as many as 6,000 people who had surgery at two medical centers in Denver and Colorado Springs might have been exposed to hepatitis C, and surgical patients at hospitals in Mount Kisco, N.Y., and Houston might have been similarly exposed. The woman reportedly worked in those communities from 2005 to 2008, though it is unclear whether she was infected with hepatitis C at that time.

The woman is being held without bond in Colorado, where a federal grand jury is investigating the claim that she switched the needles despite knowing that she had hepatitis C, the news service said.