The U.S. attorney's office in Concord has joined an investigation into a hepatitis C outbreak at Exeter Hospital in New Hampshire.

A hospital worker and 19 patients at its cardiac catheterization lab have tested positive for the liver-destroying disease since the investigation began last month. State health officials suspect a lab employee's misuse of drugs led to the outbreak.

U.S. Attorney John Kacavas said Tuesday his office has brought in personnel from the Food and Drug Administration and FBI to determine whether the outbreak is a criminal or civil matter.