The superbug that raged through Bill Warner’s body after a routine medical scope procedure in early 2013 was so dangerous that his family was warned about entering his room at a time when he needed them most.

For more than eight months after the procedure at the Carolinas Medical Center in Charlotte, N.C., the 55-year-old truck driver suffered. He hallucinated, gripped the sheets in intense pain and withered away, losing 60 pounds before dying on Nov. 24, 2013, according to testimony his wife later gave at a federal hearing.

But the hospital never filed a report required when a medical device kills or seriously injures a patient. The mandatory federal reports are meant to alert regulators to dangerous defects in devices so that lives can be saved.

A Senate investigation of deadly infections spread by contaminated scopes found that not one of the 16 or more American hospitals where patients were sickened appeared to have properly filed the required federal report.

A Senate report titled “Preventable Tragedies” said the hospitals’ failure to properly report the outbreaks left the Food and Drug Administration “with an inaccurate picture of the frequency and severity” of the outbreaks.

The FDA didn’t warn hospitals about the device until Feb. 19, 2015, after a Los Angeles Times article detailed an outbreak at Ronald Reagan UCLA Medical Center, where seven patients were infected, including three who died.

By then, at least 195 patients at hospitals across the country had been infected since the first known U.S. outbreak in 2012, according to the investigation by the minority staff of the Senate Committee on Health, Education, Labor and Pensions.

Some hospitals informally notified the scope manufacturers — and sometimes federal regulators — about the outbreaks, but those notices often came months later, according to the report released last week.

“Hospitals don’t want to be on the front page of newspapers, so they go into this quiet mode,” said Lawrence Muscarella, a medical safety expert in Montgomeryville, Pa. “There is this code of secrecy.”

Investigators said it was likely other hospitals experienced outbreaks from the device known as a duodenoscope but had never tried to identify or track them.

Because of the lack of reporting, it may never be known how many patients were sickened by the reusable devices, which regulators now say are nearly impossible to disinfect.

Doctors use the long, snake-like duodenoscope nearly 700,000 times a year in a procedure in which it is threaded down a patient’s throat and into the digestive tract to diagnose and treat cancers, gallstones and other conditions.

Last week, Olympus Corp., the leading manufacturer, said it was recalling and redesigning the duodenoscope model it began selling in 2010. Three independent experts have questioned the safety of the scope’s intricate, hard-to-clean design.

Federal law requires hospitals to report deaths from a medical device to the FDA within 10 days. If the device seriously injures a patient, the hospital must notify the manufacturer within 10 days. Both notices require hospitals to fill out what the FDA calls Form 3500A.

The staff of the Senate committee said its conversations with hospital employees during the investigation “revealed a disconcerting lack of awareness that these reporting obligations even exist.”

The FDA also allows anyone, including patients or family members, to file voluntary reports of problems with medical devices. Some hospitals eventually filed these voluntary reports with the agency.

At some hospitals, doctors launched time-consuming investigations to trace the source of their patients’ illnesses. Many hospitals contacted local health officials; some reached out to the federal Centers for Disease Control and Prevention.

But for years, other medical centers — and the public — remained in the dark to this patchwork of uncoordinated and behind-the-scenes efforts. Because there was no single repository for the reports, it was difficult to spot patterns or quickly understand why patients were falling ill.

In California, local health officials keep details on most hospital outbreaks confidential. Officials say the secrecy helps to encourage hospitals to report problems so that they can be fixed. The state requires hospitals to report unusual events such as outbreaks, but they face no financial penalty if they don’t.

The FDA began looking into the possibility that the duodenoscope could transfer bacteria between patients only when it was alerted by the CDC in September 2013 of an outbreak at an Illinois hospital. When the FDA staff looked to see whether reports of similar outbreaks had been filed, the Senate investigators said, it appeared to have found just one. By that time, eight outbreaks had happened or were continuing at American hospitals, the investigators said.

Carolinas Medical Center was among the hospitals that “failed entirely to alert” manufacturers or the FDA of the problems, according to the investigators. The hospital did not respond to repeated requests for comment from the Times.

At least five patients were sickened in an outbreak at Froedtert Hospital in Milwaukee beginning in May 2013, but a hospital official did not report the case to the manufacturer until January 2014, according to the Senate report.

Froedtert doctors eventually identified 27 patients who had procedures with the same scope and tried to contact them to undergo testing for the superbug, the hospital’s doctors later wrote in a medical journal article, which was published this year. Six of those patients could not be reached because they had died or were in hospice care, according to the article. One of the patients who tested positive for the bacteria also died, they wrote.

A Froedtert spokeswoman said the hospital did not file the mandatory report when it alerted the manufacturer because the doctors had not definitely confirmed that the scope was the source of the infections.

At the University of Massachusetts Memorial Medical Center, doctors discovered 14 patients with dangerous drug-resistant infections from September 2012 to April 2013. Ten of those patients had been treated with the scope, the hospital said.

Anthony Berry, a university spokesman, said the hospital had advised Olympus and local health officials about the outbreak in February 2013. The hospital did not file Form 3500A, he said, because testing had failed to find the same bacteria that sickened the patients on the scope.

Thomas Jefferson University Hospital in Philadelphia gave a similar reason — negative test results — for not reporting infections in eight patients. Senate investigators said those patients were sickened in early 2013.

Muscarella said the scopes can test negative but still harbor bacteria inside.

He said many hospitals have close relationships with device manufacturers. Some hospitals purchased millions of dollars in equipment from Olympus or the two other manufacturers, he said. Those expensive purchases can make hospitals reluctant to report problems, he said, because the $40,000 devices may become unusable if they are found to be flawed.

Deborah Kotz, an FDA spokeswoman, said hospitals face fines and other penalties for not meeting the legal reporting requirements.

“We have investigated cases and taken compliance actions,” Kotz said, “but we are not aware of criminal prosecutions that have resulted from a failure to report adverse events.”