Influenza, commonly called the flu, is an acute viral infection of the respiratory system, including the throat, nose, bronchial tubes, and lungs, that causes mild to severe illness and can lead to death. Through objective overviews, primary sources, and full-color illustrations, this title examines What Is Influenza? What Causes Influenza? What Are the Public Health Risks of Influenza? and Can Influenza Be Treated or Cured?