(Portland, OR)  --  Health officials are still trying to determine the source of an E. coli infection that killed an Oregon girl and sickened a boy from Tacoma.  Family members say four-year-old Serena Proffitt and the five-year-old boy shared a turkey sandwich at a restaurant in Otis, Oregon during the Labor Day weekend, but the restaurant has been ruled out as the source of the infection.  Serena was taken off life support at a Portland hospital on September 8th, and her friend remains hospitalized in Tacoma.