Influenza, or the flu, is a very common bacterial disease that most everyone is aware of. It is highly contagious and different strains come around annually. Although many cases are mild, some strains are more harmful than others. Typical symptoms include body aches, coughing, sore throat, fever, headaches, and more. Historically, influenza has been one of the worst diseases worldwide. In 1918, the Spanish flu killed more than 500,000. At the current time, about 20,000 people die annually from the flu in the United States.