LAS VEGAS - Nearly 40,000 people learned this week that a trip to the doctor may have made them sick. In a type of scandal more often associated with Third World countries, a Las Vegas clinic was found to be reusing syringes and vials of medication for nearly four years. The shoddy practices may have led to an outbreak of the potentially fatal hepatitis C virus and exposed patients to HIV, too.

The discovery led to the biggest public health notification operation in U.S. history, brought demands for investigations and caused scores of lawyers to seek out patients at risk for infections.

Thousands of patients are being urged to be tested for the viruses. Six acute cases of hepatitis C have been confirmed. The surgical center and five affiliated clinics have been closed.

"I find it baffling, frankly, that in this day and age anyone would think it was safe to reuse a syringe," said Michael Bell, associate director for infection control at the national Centers for Disease Control and Prevention.

One of the infected patients is retired airplane mechanic Michael Washington, 67, who was the first to report his infection. On the advice of his doctor, he received a routine colon exam in July at the Endoscopy Center of Southern Nevada.

In September, he started to get sick. He was losing weight fast. His urine turned dark. His stomach hurt. By January, it was clear what had happened.

Washington describes his virus as a "creeping death sentence" and worries that others will hear his story and think twice before getting preventive care they need.

In letters that began arriving this week, patients who received injected anesthesia at the endoscopy center from March 2004 to mid- January were urged to get tested for hepatitis B and C, and HIV.

Because all three viruses are transmitted by blood, they could have been passed from one patient to the next by the unsafe practices at the clinic.

The mass notification is the result of a health district investigation that began in January when officials linked an uptick of unusual hepatitis C cases to the clinic.

Health officials say they are most worried about the spread of hepatitis C, which targets the liver but shows no symptoms in as many as 80 percent of infections.

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.

Officials estimate that 4 percent of the patients already had the virus when they entered the clinic, compared with 0.5 percent for hepatitis B and less than 0.5 percent for HIV. Hepatitis C also is easier to transmit than HIV, they said.

"You put the two together and hepatitis C is really our big concern," said Brian Labus, senior epidemiologist at the Southern Nevada Health District.

Health inspectors say they observed clinic staff using the same syringe twice to extract anesthesia from a single vial, which was then inappropriately used to treat more than one patient. The practice allows contaminated blood in a used syringe to taint the vial and infect the next patient.

Of the six patients so far diagnosed with acute hepatitis C, five received treatment at the clinic on the same day in late September.

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. The doctor involved in the case acknowledged reusing syringes and settled scores of lawsuit. But he never explained why the syringes were reused.

Bell said such improper procedures appear to be more common in outpatient surgical centers like the endoscopy center. Unlike hospitals, such centers often do not have employees whose sole responsibility is to monitor and educate staff on best practices.

In Las Vegas, clinic staff told inspectors they had been ordered by management to reuse the vials and syringes. Labus described the practice as an unwritten, but long-practiced policy.

Investigators were told the practice was an attempt to cut costs, according to a letter of complaint from the city, which revoked the facility's business license Friday. Five other facilities affiliated with the Endoscopy Center of Southern Nevada also had their licenses revoked.

The clinic's majority owner, Dipak Desai, a political contributor and member of the governor's commission on health care, has refused to comment on the allegations.

He released a statement expressing concern for the patients and assuring the public the problems had been corrected. He later took out a full-page ad in Sunday's edition of the Las Vegas Review-Journal insisting that needles had not been reused and that the chances of contracting an infection at the center in most of the last four years were "extremely low."

Of the thousands of people who have rushed to be tested, many will get positive results, Labus said. More than 15,000 people already have called the health district for information.

But it takes a more sophisticated test, a complete evaluation of risk factors and a clear pattern of infection to determine whether the virus was caught at the facility.

Plenty of lawyers are wading into the mess. Television ads called "health alerts" are soliciting clients. At least a handful of class-action lawsuits have been filed.

On Tuesday, the office of Las Vegas attorney Ed Bernstein was buzzing with phone calls — nearly 1,000 a day, he said. Bernstein said he represents about 1,200 patients at the facility, eight who have tested positive for hepatitis C.

Washington, the infected airplane mechanic, is one of Bernstein's clients.

His wife, Josephine, a registered nurse, wonders how any health care professional could be so reckless: "To maximize profit? For what? What are you going to save?"