The other nurse, who was no longer employed by the clinic at the time of the CDC visit, was interviewed by telephone and reported similar practices.

The CDC concludes, as did the Southern Nevada Health District and the Nevada State Health Division, that unsafe injection practices probably resulted in six people contracting hepatitis C at the Endoscopy Center of Southern Nevada on July 25 and Sept. 21 of last year. The nurses would use a syringe on an infected patient, and then reuse the syringe to draw medication for the patient, contaminating the medication vial for patients down the line.

An investigation by health authorities that began in early January led to the largest patient notification in U.S. history. About 50,000 former patients of the 700 Shadow Lane facility are being urged to get tested for hepatitis and HIV. Tens of thousands of tests have been administered, with about 400 people testing positive. Health authorities have linked 84 of these cases, seven of them acute cases, to the closed medical clinic. An eighth acute case has been linked to a sister clinic.

The CDC sent officers from its Division of Viral Hepatitis and Division of Healthcare Quality Promotion to Las Vegas on Jan. 9 to assist with the investigation. CDC and health district investigators spent nearly a week observing procedures at the endoscopy center.

Among other unsafe practices, CDC investigators observed clinic staff "not performing proper or adequate hand hygiene between patients.'' In some cases nurse anesthetists were seen not using gloves. One nurse anesthetist was seen "moving about the room with an uncapped needle.''

Nurses also were observed pre-filling syringes with lidocaine, recapping the needles and storing them in a drawer without labeling or dating them, the report says.

All of the improper infection control practices were pointed out to staff.

The CDC also instructed the clinic's staff not to reuse detergent solution on multiple endoscopes. However, despite identifying problems with the cleaning of endoscopes, neither the CDC nor the health district linked infection transmission to the actual procedures and equipment.

The same two nurses also were responsible for giving anesthesia to a known carrier of chronic hepatitis C on each of the two dates at issue. Those patients are thought to be the sources of infection for patients treated after them.

According to the CDC report, the six patients ranged in age from 37 to 72.

Four of the five patients on Sept. 21 have been linked genetically to the potential source, health officials say. Blood results are pending on the fifth patient. Genetic testing has yet to be done on the July case.

Brian Labus, senior epidemiologist for the health district, said roughly 120 people had procedures on those two days. No other patients treated on those days have tested positive for hepatitis C, he said.

Debra Scott, executive director of the Nevada State Board of Nursing, said the CDC's report offers new details about nurse involvement in the outbreak. The report also identifies two nurses who knew of the unsafe infection control practices but did not report them. This failure could result in disciplinary action being taken against the nurses, Scott said.

Four nurses were identified by the CDC in its report. The other two nurses were not observed reusing syringes. However, one of them admitted "having been instructed to reuse syringes to administer multiple doses of propofol to an individual patient, but did not do so," the report states.

Scott said she has heard that some nurses who worked at the clinic might be remaining silent out of fear they'll be disciplined.

"We really didn't know who knew what and who actually witnessed the misconduct," Scott said. "What we're trying to figure out is where in the hierarchy did communication break down about standard practices."

The CDC's report doesn't identify who instructed nurses to reuse syringes and single-dose medication vials.

When the city of Las Vegas revoked the business licenses of the Shadow Lane facility and its affiliated clinics, the head of the licensing division said investigators learned that some doctors, including majority owner Dipak Desai, had ordered nurses to reuse syringes and single dose vials of propofol.

The six patients who had procedures on July 25 and Sept. 21 were treated by either Desai or Dr. Eladio Carrera, a part owner of the endoscopy center. The two have had their medical licenses suspended pending the investigation.

Six nurse anesthesists have voluntarily relinquished their licenses.

Contact reporter Annette Wells at awells@reviewjournal.com or 702-383-0283.