Story highlights At least 91 of the defendants in the case have been taken into custody, officials say

Federal agents say the operation uncovered $450 million in false billings

Arrests in seven metro areas wrap up an investigation of several months

More than 100 people have been charged and an estimated $450 million in false billings uncovered by federal agents in a nationwide operation that authorities say is the largest bust in recent history.

Top law enforcement officials announced the charges were lodged in seven metropolitan areas, capping an investigation of several months into efforts to defraud Medicare, Medicaid and other federal health programs.

At least 91 of the defendants in the case have been taken into custody following an early morning roundup and the execution of 20 search warrants, the officials said.

In Miami, 59 people were charged. Seven defendants were charged in Baton Rouge, Louisiana, nine were charged in Houston, eight were charged in Los Angeles, 22 were charged in Detroit, one was charged in Chicago and one in Tampa.

Authorities pointed to an alleged scheme involving community mental health centers in Baton Rouge as the largest and among the most egregious. Seven people were charged in an alleged operation that involved recruiting beneficiaries from nursing homes and homeless shelters -- some of whom were drug addicted or mentally ill -- and provided them with no services or with medically inappropriate services.

Officials from the Justice Department and the Department of Health and Human Services said most of the suspects were charged with making false claims against the Medicare program. Authorities said they participated in schemes that brought charges of conspiracy, health care fraud, violation of anti-kickback statutes and money laundering.

Those arrested include nurses, therapists, social workers and a pharmacist.

Charges against ambulance companies for billing to cover unnecessary rides represented a new wrinkle in fraud enforcement, officials said.

The law enforcement operation is the largest of four such sweeps announced during the past two years.

At a Justice Department news conference, Attorney General Eric Holder and Health and Human Services Secretary Kathleen Sebelius emphasized their determination to combat phony billing practices in the health care industry.