All three manufacturers of these scopes had redesigned of them within the last decade, enclosing a complex area at their tips to minimize contact with patients' bacteria, ABC News has learned.
"That presents cleaning challenges because it is not an open surface," Weber said. "There's a mechanism inside there. It's not easy to get the appropriate brushes into that space."
"For example, one step of the manual cleaning instructions in device labeling is to brush the elevator area," the FDA communication said. "However, the moving parts of the elevator mechanism contain microscopic crevices that may not be reached with a brush. Residual body fluids and organic debris may remain in these crevices after cleaning and disinfection. If these fluids contain microbial contamination, subsequent patients may be exposed to serious infections."
Older duodenoscope models have exposed elevator wire channels at the tips so the manufacturers -- FujiFilm, Olympus and Pentax -- each decided to enclose these channels in their newer models. Fujifilm was the first to do this in 2004, followed by Pentax in 2009. Olympus, the manufacturer named in the UCLA outbreak, was the last to do this, and had filed paperwork with the FDA only last fall, initially thinking it wasn't necessary to get clearance for the change, ABC News has learned.
"The elevator wire channel port is now sealed so separate cleaning is no longer necessary," Olympus said in a product brochure announcing the change. "The result is faster, easier cleaning that makes scope reprocessing more efficient."
When 39 duodenoscope patients became infected with antibiotic-resistant bacteria at one Illinois hospital in 2013, researchers at the CDC determined that the scopes had been cleaned properly but they found antibiotic-resistant E. coli and another bacteria around the enclosed channel two months after the scopes were last used. A manufacturer was not named in the study.
"The complicated design of duodenoscopes makes cleaning difficult," the researchers wrote in the discussion section of the study. "It appears that these devices have the potential to remain contaminated with pathogenic bacteria even after recommended reprocessing is performed."
Since the UCLA CRE cases were announced in February, Cedars-Sinai Medical Center has had four patients test positive for CRE, and Hartford Hospital in Connecticut has announced that 300 of its patients were exposed to E. coli. Both exposures were linked to duodenoscopes.
Still, neither doctors nor health officials want to pull the scopes because these infections are rare, and the devices allow doctors to treat patients with deadly diseases and infections without surgery, increasing their chances of survival.
Duodenoscope procedures are not elective, and usually necessitated by a serious symptom, Weber said.
"The value of the procedures performed utilizing these devices far outweighs the unfortunate events that have occurred," said Dr. Michael Kochman, who chairs the American Gastroenterological Association's Center for GI Innovation and Technology.
FujiFilm declined to comment, and neither Olympus nor Pentax were immediately available for comment.
Olympus said in a prior statement to ABC News that it is aware of reports involving its duodenoscopes, and it is working with the FDA, medical organizations and customers to address concerns. It is also making supplemental educational materials available to customers.
"While all endoscopes, including duodenoscopes, require thorough reprocessing after patient use in order to be safe, the Olympus TJF-Q180V requires careful attention to cleaning and reprocessing steps, including meticulous manual cleaning, to ensure effective reprocessing," the company said.