A deadly outbreak of superbugs has Congress once again questioning whether the Food and Drug Administration is letting unsafe medical devices slip through the cracks.

The agency didn't fully approve a complex instrument called a duodenoscope that infected 11 people and killed two at Cedars Sinai and University of California-Los Angeles Medical Center last month. It wasn't the first time the FDA has failed to properly clear an unsafe device before it hit the market.

A group of 11 House members wrote to the agency last month asking questions about why the scopes weren't properly regulated. Sen. Patty Murray, a Democrat from Washington state, also chided outgoing FDA Commissioner Margaret Hamburg for not doing more to oversee the scopes.

Hamburg admitted during her farewell address last week that the U.S. didn't get the medical device review process "completely right." She declined to elaborate on what exactly was wrong about the process.

The duodenoscope, a narrow tube used to take tissue samples or look for disease, was cleared initially by an FDA pathway for devices that are similar to one already on the market.

Under the expedited process, a device maker doesn't have to provide the same level of safety and effectiveness data for new devices.

In Olympus' case, the scope was cleared, but the company later made modifications to it. The company didn't think the modifications warranted a new application, but the FDA disagreed.

However, the agency declined to take the scope off the shelves while the modifications were being reviewed due to the demand for its use in medical procedures. The agency has estimated the scopes are used in more than half a million procedures a year.

Currently Olympus is the only duodenoscope with an application pending, FDA spokeswoman Jennifer Dooren told the Washington Examiner.

Two other companies, FujiFilm and Pentax, also make duodenoscopes.

This isn't the first time the FDA has gotten in trouble for lax oversight of devices. In 2012, Bloomberg reported the FDA didn't clear a Johnson & Johnson vaginal mesh for five years because the company decided the changes didn't warrant new approval.

The agency looked into the mesh only after the company was hit with a string of lawsuits due to alleged injuries, according to Bloomberg.

The citizen advocacy group Public Citizen called for the pathway to be dismantled and replaced with one that requires more clinical testing for safety and effectiveness.

"This is particularly important for devices that are intended to be life-sustaining or life-saving or are to be permanently implanted," said Dr. Michael Carome, head of Public Citizen's Health Research Group.

Carome couldn't say how common it is for device makers not to seek FDA approval for a modified device, but "this is certainly not the first time a company has failed to do so."

However, the pathway actually gives the FDA more leeway to require additional data for safety and efficacy if the agency has concerns, one supporter said.

"Even though [the FDA is] just approving substantial equivalence, FDA is still looking at whether the device is safe or effective," Jonathan Kahan, a partner with the law firm Hogan Lovells who has represented medical device companies, told the Washington Examiner.

The FDA told the Examiner that it is taking steps to address the outbreak, including working with all duodenoscope manufacturers on how to improve the design of the devices so they can be better cleaned. The hospitals said they followed the manufacturer's cleaning instructions, but the scopes still infected people.

The agency also will ask companies to submit more cleaning instruction data when they submit a new scope for regulatory approval, Dooren said.