The flu is a contagious respiratory illness caused by the influenza viruses that infect the nose, throat, and sometimes the lungs. Most infectious disease experts believe that flu viruses spread mainly by droplets made when people with the flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. A person might also get the flu by touching a surface or object that has the flu virus on it and then touch their own mouth, nose, or eyes.