An American health care worker is back in the U.S. to receive treatment after becoming infected by the Ebola virus while working in Sierra Leone. Authorities have not released details about the worker’s identity or what organization they were with. The health care worker will receive care at the same unit in Bethesda, Maryland that successfully treated nurse Nina Pham when she became infected with the virus last fall. At least 10,000 people in West Africa have been killed during the outbreak, though prevention and treatment efforts are helping to stop its spread …