A nurse helps a recovering severe acute respiratory syndrome (SARS) patient as she leaves the Shin Kong Memorial Hospital in Taipei in 2003. SARS is a viral infection that caused a major epidemic between November 2002 and July 2003. Over a few months, the illness spread to more than 24 countries in North America, South America, Europe and Asia, causing more than 8,000 known infections and 774 deaths. (© AP Images)