Tainted medical scopes at a UCLA medical center may have exposed up to 179 people to a potentially deadly superbug that has already been linked to two deaths, a hospital spokeswoman told FRONTLINE.

Superbugs are antibiotic-resistant bacteria that kill up to 23,000 Americans each year. In the UCLA outbreak, which took place at the university’s Ronald Reagan Medical Center from October to January, seven people are already confirmed to have been infected, including the two who died, said spokeswoman Elaine Schmidt.

Many of the potentially exposed patients were undergoing a procedure to diagnose and treat disorders that included problems with the pancreas and biliary tract, UCLA said. UCLA began notifying patients of the outbreak on Wednesday, and they are being offered free home testing kits that the hospital has agreed to analyze.

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UCLA said the contaminated instruments had been sterilized to the manufacturer’s standards, but may nonetheless have transmitted carbapenem-resistant Enterobacteriaceae (CRE). CRE is a family of bacteria that lives in the gut and is resistant to practically every antibiotic on the market today, including carbapenems, which are widely considered antibiotics of last resort.

On Thursday, the Food and Drug Administration warned that the design of the devices, called duodenoscopes, could impede the detailed process of cleaning and disinfecting. The scopes are lit, flexible tubes that are threaded through the mouth, throat, stomach, and duodenum. The FDA recommended new maintenance procedures, and not using scopes that may have been tainted.

UCLA said in a statement that it stopped using the two scopes involved in the outbreak and is now using a decontamination process that goes “above and beyond the manufacturer and national standards” for its scopes.

The Centers for Disease Control and Prevention considers CRE an urgent threat. It reports that more than 9,000 CRE infections each year are linked to healthcare facilities, and that some form of CRE has been found in almost every state. Approximately 600 people die each year from the two most common types of CRE, according to the CDC.

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Similar CRE exposures have been reported in other U.S. hospitals that use the same type of scopes, UCLA said. Between 2012 and 2014, for example, contaminated scopes were blamed for infecting at least 32 patients at Virginia Mason Medical Center in Seattle. Eleven of those patients died, but doctors said it was unclear what role the infections may have played, The Seattle Times reported.

FRONTLINE’s Hunting the Bacteria looks at the dangers of superbugs in hospitals:

(Editor’s note: An earlier version of this story referred to the contaminated medical devices as stethoscopes; UCLA says they were a different type of scope used in endoscopic procedures.)