* Mistakes cost Medicare $324 million in a single month

* 134,000 adverse events in month studied

WASHINGTON, Nov 16 (Reuters) - Mistakes and unavoidable problems kill an estimated 15,000 elderly U.S. patients every month in hospitals, U.S. government investigators reported on Tuesday.

More than 13 percent of patients covered by Medicare, the government health insurance for the elderly, or about 134,000 people monthly have some sort of so-called adverse event each month. These include mistakes such as surgical errors or sometimes unavoidable problems such as an infection spread in the hospital, or patients having their blood sugar fall to unusually low levels.

The new numbers, which total about 180,000 deaths a year, were presented in a report by the Office of Inspector General at the Health and Human Services Department. They support findings of a landmark Institute of Medicine report in 2000 that said up to 98,000 Americans died every year because of medical errors.

"An estimated 13.5 percent of hospitalized Medicare beneficiaries experienced adverse events during their hospital stays," the OIG said in the report, availablehere.

It said 44 percent of the problems were avoidable.

The OIG team worked by examining a nationally representative random sample of 780 Medicare beneficiaries discharged from a hospital in October 2008.

“Hospital care associated with adverse and temporary harm events cost Medicare an estimated $324 million in October 2008,” the report concludes.

President Barack Obama has said his signature healthcare reform legislation will help reduce errors with measures such as wider use of electronic medical records.

Consumers Union, which publishes Consumer Reports magazine, said patients needed ways of learning which hospitals make the most errors.

“This report shows that hospital patients are being harmed by medical errors at an alarming rate. Unfortunately, most Americans have no way of knowing whether their hospital is doing a good job preventing medical errors,” the group’s Lisa McGiffert said in a statement.

The OIG report recommends that two HHS agencies -- the Agency for Healthcare research and Quality and the Center for Medicare and Medicaid Services -- should do more to encourage reporting of adverse events, and broaden the definition so that trends can be identified.

Both agencies said they would.

Rich Umbdenstock, president of the American Hospital Association, said hospitals would work to improve.

“Hospitals are already engaged in important projects designed to improve patient care in many of the areas mentioned in the report. We are committed to taking additional needed steps to improve patient care,” Umbdenstock said in a statement. (Editing by Cynthia Osterman)