If you develop fever and flu-like symptoms within 10 days after coming back from the USA, Mexico and Canada, you need to contact the folling center.
http://www.u-tokyo.ac.jp/gen03/public11_e.html (General information) http://www.hc.u-tokyo.ac.jp/t09announce1-e.htm (Notice from U-Tokyo Health Service Center)

Please note that you cannot visit the University health Center if you visited these countries and have fever