According to the Center for Disease Control and Prevention (CDC ), influenza (flu) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. There are two main types of influenza (flu) viruses: Types A and B. The influenza A and B viruses that routinely spread in people are responsible for seasonal flu epidemics each year. Most experts believe that flu viruses spread mainly by tiny droplets made when people with the flu cough, sneeze or...