The U.S. Justice Department has joined a whistle-blower case against Prime Healthcare Services, adding significant weight to allegations of widespread Medicare overbilling at 14 of the company’s hospitals in California. A Los Angeles magistrate judge granted the agency’s request to intervene in the case Tuesday, one day after the government declared in a court filing that its investigation of the Ontario- hospital operator has “yielded sufficient evidence” that the facilities “submitted or caused the submission of claims to Medicare for unnecessary inpatient stays.”