Concern about the Ebola outbreak in West Africa has prompted a heightened response from the Centers for Disease Control and Prevention. The federal health agency imposed tight security and safety precautions as the first Americans infected with the virus arrived in the United States from Liberia, where they had been working. Dr. Kent Brantly arrived on Saturday in Atlanta for treatment at Emory University Hospital, and Nancy Writebol is due to arrive on Tuesday. CNN reports that both received doses of an experimental drug. The report could lead to calls for wider use of the product, which has not been approved for use, based on anecdotal reports about promising results in the two patients.