The Food and Drug Administration on Thursday warned doctors and hospitals that a commonly used type of medical scope can be difficult to sanitize between uses and “may facilitate the spread of deadly bacteria.”

The agency’s warning came a day after news broke that seven patients had been infected by a drug-resistant “superbug” at UCLA’s Ronald Reagan Medical Center since last fall. Two of the patients died, and public health authorities are tracking down nearly 200 others who might have been exposed to the dangerous bacteria through the use of the contaminated medical scopes.

Known as duodenoscopes, the devices are used in hundreds of thousands of procedures each year in the United States to drain fluids from pancreatic and bile ducts blocked by cancer tumors, gallstones and other conditions. Doctors consider them an important tool in detecting and treating medical problems early and in a minimally invasive way.

The California outbreak, first reported by the Los Angeles Times, represented the latest in a string of lethal superbug episodes linked to the specialized scopes.

Since 2012, similar outbreaks have occurred at Advocate Lutheran General Hospital near Chicago, where 44 people were infected, and at the Virginia Mason Medical Center in Seattle, where at least 32 patients became ill and 11 died. It’s unclear how significant a role the bacterial outbreak played in those deaths, but the Seattle hospital stressed that the instruments were cleaned according to the manufacturer’s stipulations.

This illustration depicts a three-dimensional computer-generated image of a group of carbapenem-resistant Enterobacteriaceae (CRE) bacteria. The UCLA Health System said seven patients were infected with a potentially deadly, drug-resistant strain of bacteria at Ronald Reagan UCLA Medical Center. (Melissa Brower/AP/CDC)

Lawmakers and patient-safety experts have increasingly pressed the FDA and device manufacturers to issue warnings about the problem and take steps to fix it. The Centers for Disease Control and Prevention alerted the FDA to the potential problem in the fall of 2013. Over the past two years, the FDA has received at least 75 reports of incidents involving at least 135 patients. Sen. Patty Murray (D-Wash.) earlier this month wrote to FDA Commissioner Margaret Hamburg, urging the agency to publicly address the issue. Until Thursday, that had not happened.

“The FDA is not doing its job,” said Lawrence Muscarella, a hospital-safety consultant and expert on endoscopes who has been monitoring the problem in recent years. “It’s really not acceptable. . . . These reports have been coming for at least 3 to 5 years.”

The FDA said in a statement that it has been working closely with the CDC, device manufacturers and others “to better understand the issues that contribute to the infections and what can be done to mitigate them.” By Thursday, the agency said, officials “now have enough of an understanding of the issues to communicate publicly and to provide recommendations.”

The agency noted that hundreds of thousands of ill patients have benefited from the use of the scopes and that the devices have been associated with the transmission of bacteria in only a small number of instances. “The FDA believes the continued availability of these devices is in the best interest of public health,” the agency said.

The bacteria at the center of the Los Angeles outbreak are known as CRE, or carbapenem-resistant Enterobacteriaceae, strains of which have become resistant to nearly all kinds of antibiotics. There are an estimated 9,300 cases of CRE each year in the United States that kill 610 patients, according to a 2013 report from the CDC. The bacteria kills “up to half” of patients who contract CRE bloodstream infections, the agency said.

During a typical procedure, a flexible and lighted tube is threaded through the mouth, throat and stomach and into the top of the small intestine. Unlike other endoscopes, duodenoscopes have a movable “elevator” mechanism at one end that allows the instrument to maneuver into ducts and fix fluid-drainage problems.

That intricate design can make the devices difficult to sterilize. Cleaning the scopes is “a detailed, multi-step process,” and meticulously following the directions for disinfecting them “should reduce the risk of transmitting infection but may not entirely eliminate it,” the FDA said Thursday.

The agency urged medical workers to closely follow instructions for cleaning the devices and to report any problems to the FDA and manufacturer. It urged doctors to tell patients about the risks — something patient advocates say happens too rarely. For now, the agency has not asked manufacturers to redesign the devices.

In recent years, hospitals have had to resort to extreme measures in their struggle against superbugs. In 2011, the National Institutes of Health Clinical Center built a wall to isolate patients, gassed rooms with vaporized disinfectant and ripped out plumbing, in an attempt to stop the spread of a deadly outbreak of the antibiotic-resistant bacteria. It eventually spread to 18 patients, 11 of whom died; seven of those deaths were directly attributed to the superbug. The NIH did not make the outbreak public until it described it in a scientific publication a year after the outbreak.

Lena H. Sun, Jason Millman and Lindsey Bever contributed to this report.