The federal Centers for Disease Control and Prevention has yet to conclude the investigation it began last September of why four transplant patients at UPMC contracted mold infections and later died. But its 17-member investigative team made clear in a “Notes from the Field” report it put online Thursday that it is still focused on the negative pressure room that three of the four patients stayed in at UPMC Presbyterian — and it is recommending that other hospitals not do what UPMC did.