You run into a friend you haven$$t seen since $2000$ and you decide to go to lunch. While you are regaling each other with your various stories, she tells you about this horrible illness she picked up while visiting Toronto in winter of $2003.$ She had a high fever, dry cough, and difficulty breathing. She also had some mild stiffness, although it wasn$$t too bad. When she went into the emergency room, the doctor thought it was pneumonia and prescribed a cephalosporin, but that did not work. After several days to a week your friend felt better and eventually fully recovered. You respond to her story in amazement and tell her that she was lucky that she hadn$$t died like several other people in Toronto did. What do you suspect your friend had? What is the causative agent?