(CNN) -- Public health officials urged Wednesday that anyone who may have been treated at a hospital's heart lab in southeastern New Hampshire since October 1, 2010, be tested for a virus that can cause liver disease.
The alert was issued after 20 people who either worked at or were treated at Exeter Hospital's Cardiac Catheterization Laboratory tested positive for hepatitis C, the state's public health director told reporters.
"These new test results are not surprising," said Dr. José Montero, director of New Hampshire Health and Services. "We know that this is a very troubling situation and our thoughts go out to all those who have been affected."
Officials suspect an infected hospital employee diverted part of a drug dose by injecting it into himself or herself and then administered the remaining portion to patients via the same needle, Montero said.
All 20 of those known to have been infected with the same strain of virus have been told of their status, he said.
The suspect has not been identified publicly. "The investigation is still ongoing," said Montero, adding that testing continues. "We still may find more cases of hepatitis C that match this strain," he said.
Officials are recommending anyone treated at the lab since October 1, 2010, be tested for the virus. Of more than 700 samples examined, 26 tested positive, but six were a different strain of hepatitis C than the one carried by the suspect and were unrelated to the outbreak, he said.
In all, hospital officials plan to test more than 900 people.
According to the Centers for Disease Control and Prevention, liver disease caused by hepatitis C results in 12,000 deaths in the country each year.