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.
A routine investigation process found that practitioners at the Endoscopy Center were using the same syringe on more than one patient -- exposing those patients to the blood of other patients, reports CBS News affiliate KLAS-TV in Las Vegas.
"During the course of the investigation, we identified serious problems with the center's injection practices. We found the re-use of syringes on a patient and the re-use of vials labeled for single patient use. The combination of these two practices could have exposed patients to the blood of other patients," Brian Labus with the Southern Nevada Health District told KLAS.
Hepatitis C is 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.
Health officials are also recommending that Endoscopy Center patients also be tested for HIV, the virus that causes AIDS, reports KLAS.