A “superbug” outbreak suspected in the deaths of two Los Angeles hospital patients is raising disturbing questions about the design of a hard-to-clean medical instrument.

At least seven people _ two of whom died _ have been infected with a potentially lethal, antibiotic-resistant strain of bacteria after undergoing endoscopic procedures at Ronald Reagan UCLA Medical Center between October and January. And more than 170 other patients may have been exposed as well, university officials said.

UCLA said the infections may have been transmitted through at least two contaminated endoscopes that were used to diagnose and treat pancreatic and bile-duct problems.

The infections occurred even though the instruments had been cleaned according to the manufacturer's instructions, the hospital said.

The episode is the latest in a series of outbreaks involving such instruments.

“You can very easily do everything right and still have some contamination,” said Dr. Deverick Anderson, an infectious-disease expert at Duke University. “We're finding this is a problem, but it's probably one that we don't have a very good solution to right now.”

Lawrence Muscarella, an infection-control expert, said the recent incidents point to a design flaw that needs to be addressed.

An endoscope _ or more specifically in this case, a duodenoscope -- is a thin, flexible fiber-optic tube that is inserted down the throat to enable a doctor to examine an organ. It typically has a light and a miniature camera.

On Thursday, the U.S. Food and Drug Administration issued an advisory warning doctors that even when a manufacturer's cleaning instructions are followed, infectious germs may linger in the devices. Their complex design and tiny parts make complete disinfection extremely difficult, the advisory said.

In a statement, the FDA said is trying to determine what more can be done to reduce such infections. But it said that pulling the device from the market would deprive hundreds of thousands of patients of “this beneficial and often life-saving procedure.”

The company that supplied UCLA's equipment, Olympus Medical Systems Group, did not immediately respond to an email request for comment.

The germ is known as carbapenem-resistant Enterobacteriaceae, or CRE, and similar outbreaks have been reported in hospitals around the nation. They are difficult to treat because some varieties are resistant to most known antibiotics.

Healthy people usually don't get CRE infections; infections typically occur in patients in hospitals, nursing homes and other health care settings.

By one estimate, CRE can contribute to death in up to half of seriously infected patients, according to the U.S. Centers for Disease Control and Prevention.

CRE can cause infections of the bladder or lungs. Symptoms can include coughing, fever and chills. (AP)