The Justice Department announced charges against 15 people, including six medical professionals, in California cases involving an alleged $2 billion in fraudulent health care claims submitted to public and private insurers.

The largest case concerns $1.6 billion in billings for substance abuse treatment in Southern California. Prosecutors allege patients were recruited from across the country with offers including free flights and housing, then moved among facilities run by Los Angeles residents Nathan Young, 39, and his father, David Young, 71, whether or not they needed or received treatment.

The department said patients with premium insurance received upscale accommodations, while others were housed in cramped, unsanitary conditions. It also described separate cases involving $134 million in allegedly unnecessary arterial procedures that injured patients and $138 million in allegedly fraudulent Medicare hospice billings for patients whom prosecutors said were not terminally ill.