Authorities can't say for sure how the 77 people were infected, said Brian Labus, senior epidemiologist with the Southern Nevada Health District. But they know each was treated from March 2004 to Jan. 11 this year at the Endoscopy Center of Southern Nevada.

"We know they didn't have a positive test before they went to the clinic, and now they're positive," Labus said.

The reports bring the number of cases linked to clinics run by the same group of doctors to 85.

In the eight cases identified earlier, seven were linked to the Endoscopy Center of Southern Nevada. The other case was traced to a sister clinic, Desert Shadow Endoscopy Center.

While 300 other patients also tested positive and were interviewed, officials determined they could have contracted the virus through other means, including intravenous drug use, blood transfusions, organ transplants and kidney dialysis.

The clinics were headed by doctors Dipak Desai and Eladio Carrera, whose Nevada medical licenses have been suspended pending hearings by the state Board of Medical Examiners.

Authorities have said at least 50,000 patients may have been exposed to unsafe practices by clinic staff who reused syringes and single-use vials of medication during anesthesia.

Hepatitis C results in the swelling of the liver and can cause stomach pain, fatigue and jaundice. It may eventually result in liver failure. Even when no symptoms occur, the virus can slowly cause damage to the liver.