RENO, Nev. - A hepatitis C outbreak was caused by workers improperly reusing syringes and medicine vials at a Las Vegas clinic, federal health officials said Friday.

The Centers for Disease Control and Prevention was contacted by state health officials earlier this year after two people treated at the now-closed Endoscopy Center of Southern Nevada were diagnosed with hepatitis C.

Officials have linked 84 cases of the liver disease to the clinic after notifying 50,000 patients of the clinic to be tested.

CDC investigators said in a report to the Nevada State Health Division that during visits to the clinic, they saw employees reusing syringes to give a sedative and that interviews suggested it was common practice.

"This was considered the most likely mode of transmission," the report said.

The CDC said the same syringe was used for an individual patient if more sedative was needed. Backflow into the syringe from an infected patient could have contaminated the sedative vial. The virus could have been passed along from the contaminated vial when it was improperly used for the next patient, the CDC said.

About 400 former patients of the center tested positive for hepatitis C but officials have determined that most could have contracted the virus through other means, including intravenous drug use, blood transfusions, organ transplants or kidney dialysis, receiving blood clotting agents before 1987, or sexual contact with a person with hepatitis C.

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 damage the liver.

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

Las Vegas police have seized medical records from the clinics, and the FBI, the state attorney general and the Clark County district attorney are involved in a criminal investigation. The owners of the clinics have surrendered business licenses and paid $500,000 in fines.

Since 1999, the CDC counts 14 hepatitis outbreaks in the U.S. linked to bad injection practices.

The largest outbreak occurred in Fremont, Neb., where 99 cancer patients were infected at an oncology center from 2001 to 2002. At least one died.