MONROVIA, LIBERIA — Missionary doctor Rick Sacra working for SIM USA in Liberia tested positive for the Ebola virus and was flown to Nebraska Medical Center in Omaha on Sept. 5 for advanced treatment.  The American doctor was treating obstetrics patients at SIM’s ELWA hospital in Monrovia. He was not treating Ebola patients in ELWA’s Ebola isolation unit, a…