SANTA ANA, Calif. -- Orange County prosecutors say four people have been convicted of crimes relating to a $154 million medical fraud scheme in which hundreds of healthy patients underwent unnecessary surgeries to fraudulently bill insurance companies.

Farrah Emami, a spokeswoman for the Orange County district attorney's office, says 64-year-old Roy Dickson, 58-year-old Andrew Harnen, 63-year-old Dee Francis and 66-year-old Rosalinda Landon were found guilty of multiple tax fraud counts.

The four were convicted for their roles in recruiting more than 250 healthy patients to undergo sometimes dangerous surgeries to fraudulently bill insurance companies.

The four were among 19 defendants charged in the case, which has been divided into several trials because of its size.

A total of 13 have been indicted by a grand jury and six others pleaded guilty prior to indictment.