LOS ANGELES -- More than 40 people have been indicted in a $4.6 million scam involving nurse imposters who provided unqualified care to disabled patients -- mostly children, according to authorities.

Thursday's bust marks the largest such case ever in California.

The indictment charges 42 people of conspiring to bill the state program for in-home licensed nursing services.

Investigators say over the past two years, the fake nurses were sent to low-income homes to provide care for patients such as children with Cerebral Palsy and others who need constant, trained medical care. They also used the names of actual Registered Nurses, according to investigators. The individuals all worked in Los Angeles, Orange and Riverside Counties, officials said.

In some cases, the fake nurses put patients' lives at risk, and "put greed and self-interest" above everything else, said lead-investigator Glenn Ferry.

In one instance, a nurse was unable to replace a tracheotomy tube that fell out of a young patient's neck. Authorities say the mother was home at the time and saved her child's life.

In another case, a tracheotomy tube was disconnected and when the female nurse couldn't give the patient proper treatment, she allegedly ran away.

Twenty people were arrested Thursday including Evelyn Tisoy who is accused of managing the nursing service in question.

The others named in the indictment are not consider flight risks and will be summoned to appear in court in the coming weeks.

Charges include conspiracy to commit health care fraud, fraud, and aiding-and-abetting. It wasn't immediately known if any of the defendants had retained attorneys.

Authorities say the nurse imposters were sent to the homes of unsuspecting Medi-Cal patients by a group called "Medcare Plus Home Health Providers," owned and operated by Priscilla Villabroza.

U.S. Attorney Thomas O'Brien says Villabroza billed Medi-Cal for nursing services and was reimbursed somewhere on average between $20 to $35 an hour per nurse, but she only paid her employees $8 to $12 an hour.

"We believe that this is the largest single case alleging Medi-Cal fraud ever filed in the state of California," O'Brien said. The scam "not only cheated taxpayers, they endangered the lives of young people they promised to protect and care for."

Villabroza pleaded guilty last August to five counts of health care fraud. She faces up to 50 years in prison and is set to be sentenced later this year.

Law enforcement officials said the case highlights the widespread abuse of the state's $34 billion Medicaid program that provides health care for more than six million people including the elderly, disabled and low-income families.

More than $330 million has been recouped over the past couple of years from criminal and civil actions dealing with Medi-Cal fraud, according to Joseph Fendrick, a special agent with the California Department of Justice.

Authorities said some of the nurses who worked for Medcare, based in Santa Fe Springs had medical training overseas, while others had no experience at all.