WASHINGTON — An outbreak of hepatitis C at a Nevada clinic may represent “the tip of an iceberg” of safety problems at clinics around the country, according to the head of the Centers for Disease Control and Prevention.

The city of Las Vegas shut down the Endoscopy Center of Southern Nevada last Friday after state health officials determined that six patients had contracted hepatitis C because of unsafe practices, including clinic staff reusing syringes and vials.

Nevada health officials are trying to contact about 40,000 patients who received anesthesia by injection at the clinic between March 2004 and January 11 to urge them to get tested for hepatitis C, hepatitis B, and HIV.

At least initially they didn’t have correct addresses for 1,400 patients, Nevada health officials said.

The Senate majority leader, Harry Reid of Nevada, met Monday with the CDC head, Dr. Julie Gerberding, and on a media conference call after their meeting both strongly condemned practices at the clinic.

Health care accreditors “would consider this a patient safety error that falls into the category of a ‘never event,’ meaning this should never happen in contemporary health care organizations,” Dr. Gerberding said.

“This is the largest number of patients that have ever been contacted for a blood exposure in a health-care setting. But unfortunately we have seen other large-scale situations where similar practices have led to patient exposures,” Dr. Gerberding said.

“Our concern is that this could represent the tip of an iceberg and we need to be much more aggressive about alerting clinicians about how improper this practice is,” she said, “but also continuing to invest in our ability to detect these needles in a haystack at the state level so we recognize when there has been a bad practice and patients can be alerted and tested.”

Reid said he would work with Gerberding to try to get the CDC more resources in an emergency spending bill Congress is to take up in April.