TULSA, Oklahoma - After thousands of tests, and dozens of positive results, investigators say they've pinpointed just one case of hepatitis they know came from Dr. Scott Harrington's office.

The dentist is being sued by a number of patients, accusing him of unsafe and unsanitary practices and possibly exposing them to disease.

The Tulsa Health Department says 89 of Harrington's former patients tested positive for hepatitis C. We spoke to the attorney of one patient who said he has proof his client's virus came from the doctor's office.

For the past six months Harrington's Tulsa and Owasso offices have been closed for business. Since then, many have sued the dentist claiming he exposed them to potentially-deadly viruses.

The health department says genetic tests done by the CDC prove one of Harrington's patients transmitted hepatitis C to another patient.

"If this is a confirmation of a patient-to-patient transfer, it likely happened on the same day that my client was there," said attorney Mark Lyons.

Lyons said his client can pinpoint when he was infected with hepatitis C.

"My client had a long history of clean blood donations to the Red Cross," Lyons said.

But Lyons said that all changed after his client got a tooth extracted at Harrington's office. According to the lawsuit, the patient donated blood in May 2012.

The blood tested negative for hepatitis C.

In July, he had dental work done at Harrington's office. One month later, he gave blood to the Red Cross and, according to the lawsuit, that blood tested positive for the virus.

"Because we know that he has zero risk factors for hepatitis C, other than through Dr. Harrington's office, it wouldn't surprise me if this is my client," Lyons said.

On Tuesday, Harrington's lawyer told us these allegations are simply allegations and his client will be fighting to get his license back.

"He misses the practice, he loves the practice and he hopes one day to be back in the practice," said attorney James Secrest, II.

Some of Harrington's former patients don't think he should be able to practice. And Lyons believes he has solid evidence that will support the allegations.

"I have every reason to think that my lawsuit is probably the cleanest one out there," Lyons said.

Even though a handful of people tested positive for hepatitis B, the health department says it has no reason to believe anyone contracted the virus from Harrington's office.

The results for the HIV tests won't be ready for several weeks.