WASHINGTON - Government investigators have found vast numbers of questionable Medicare diagnoses -- some involving unlikely claims for bubonic plague, cholera and leprosy -- potentially resulting in as much as $1 billion in fraud, waste and abuse.

A congressional report being released today found that review procedures for the Medicare Part B program, through which the government provides reimbursements for medical equipment and supplies, have not been effective in preventing fraud.

For example, investigators found hundreds of thousands of claims for blood glucose test strips -- used by diabetics -- in which the diagnoses were bubonic plague, cholera, or leprosy. There are an average of 10 to 20 U.S. plague cases a year, said the Centers for Disease Control and Prevention. For leprosy, the average is about 130.

This is in addition to billions of dollars of allegedly fraudulent Medicare claims uncovered in a series of studies commissioned by Minnesota Sen. Norm Coleman, the ranking Republican on the Senate's Permanent Subcommittee on Investigations. "This review process simply doesn't check to see whether the claim makes sense," he said.

The report said that while Medicare reviewers are required to ensure that each claim carries a specific code relating to a valid diagnosis, the reviewers didn't check to make sure the diagnoses were related to the purchased medical equipment.

The Centers for Medicare and Medicaid Services (CMS), the agency that regulates the program, estimated that questionable diagnosis codes were used to secure payments of $700 million for medical supplies in 2007. But it said that just because some of the diagnosis codes were questionable, it didn't mean the payments were improper.