How does the Flu spread?
You can get the flu if someone around you who has it coughs or sneezes. Or, you can get it simply by touching a surface, like a telephone or doorknob, that has been contaminated by someone who has the flu. The viruses can pass through the air and enter your body through your nose or mouth, or if you’ve touched a contaminated surface, they can pass from your hand to your nose or mouth. You are at greatest risk of getting infected in highly populated areas, such as in crowded living conditions and in schools.
via What You Need to Know About the Flu – How Does the Flu Spread?.