A Las Vegas clinic may have infected a handful of patients with hepatitis C, and some 40,000 more should be tested for the blood-borne virus, health officials said Wednesday.

Six people who underwent procedures at the Endoscopy Center of Southern Nevada have contracted hepatitis C, the Southern Nevada Health District said in a statement.

Five of those received treatment at the facility on the same day in late September. The sixth is believed to have been infected in July, the district said.

An investigation determined that "unsafe injection practices related to the administration of anesthesia medication might have exposed patients to the blood of other patients," the statement said.

Officials said the unsafe practices had been in place for several years and may have put others at risk. About 40,000 patients who received injections of anesthesia at the clinic are being notified of the potential exposure in letters arriving next week.

Chief health officer Lawrence Sands said anyone who received anesthesia at the clinic from March 2004 to Jan. 11 should be tested for the virus, along with hepatitis B and HIV.

"We are recommending all patients during this timeframe to get tested because we cannot determine which patients may have been exposed," Sands said.

Hepatitis C is a a chronic, potentially lethal virus that can cause liver ailments, including cancer and liver failure. The health district says it typically receives reports of two acute cases each year. Three of the six cases reported this year are acute, it said.

The district said the virus may have been spread when clinic staff reused syringes and used a single dose of anesthesia medication on multiple patients.

Endoscopy Center of Southern Nevada has ceased those practices, it said.

"All concerns noted by the health department were addressed immediately. We want to be sure that every patient who may have been exposed is informed and tested," the center said in a statement.

To retain its state license and Medicare certification, the facility faces increased on-site inspections and fines that have yet to be determined.