WASHINGTON (Reuters) — Ninety-one people including doctors, nurses and other medical professionals were charged criminally after an investigation of Medicare fraud that involved $430 million in false billing in seven cities, officials said on Thursday.

It was the government’s second big raid in recent months after a similar investigation in May involving $452 million in possible fraud in Medicare, the health program for the elderly and disabled.

The accusations include billing the government for unnecessary ambulance rides in California, writing prescriptions for patients in Dallas who did not qualify for them and paying kickbacks like food and cigarettes to patients in Houston if they attended programs for which a hospital could bill.

The investigation is part of an effort by the Obama administration to find health care savings.

Indictments against the 91 defendants were unsealed on Thursday after a coordinated investigation led by the departments of justice and of Health and Human Services, officials said. Most of the 91 surrendered or were arrested.