WASHINGTON — Nursing facilities have failed to report thousands of serious cases of potential neglect and abuse of seniors on Medicare even though it’s a federal requirement for them to do so, according to a watchdog report released Wednesday that calls for a new focus on protecting frail patients.

Auditors with the Health and Human Services inspector general’s office drilled down on episodes serious enough that the patient was taken straight from a nursing facility to a hospital emergency room. Scouring Medicare billing records, they estimated that in 2016 about 6,600 cases reflected potential neglect or abuse that was not reported as required. Nearly 6,200 patients were affected.

“Mandatory reporting is not always happening, and beneficiaries deserve to be better protected,” said Gloria Jarmon, head of the inspector general’s audit division.

Overall, unreported cases worked out to 18% of about 37,600 episodes in which a Medicare beneficiary was taken to the emergency room from a nursing facility in circumstances that raised red flags.

Responding to the report, Administrator Seema Verma said the Centers for Medicare and Medicaid Services does not tolerate abuse and mistreatment and slaps significant fines on nursing homes that fail to report cases.

Verma said the agency, known as CMS, is already moving to improve supervision of nursing homes in critical areas such as abuse and neglect and care for patients with dementia.

CMS officially agreed with the inspector general’s recommendations, including clearer guidance to nursing facilities about what kinds of episodes must be reported, improved training for facility staff, and requirements that state nursing home inspectors record and track possible problems as well as incidents reported to law enforcement.

Neglect and abuse of elderly patients can be difficult to uncover. Investigators say many cases are not reported because vulnerable older people may be afraid to tell even friends and relatives much less the authorities. In some cases, neglect and abuse can be masked by medical conditions.

The report cited the example of a 65-year-old woman who arrived at the emergency room in critical condition. She was struggling to breathe, suffering from kidney failure and in a state of delirium. The patient turned out to have opioid poisoning, due to an error at the nursing facility. The report said a nurse made a mistake copying doctor’s orders, and the patient was getting much bigger doses of pain medication as a result.