Wintertime Ailment is often referred to as the FLU, which is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe symptoms, and in some cases can even lead to death. Symptoms of the FLU include fever, chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and sometimes vomiting and diarrhea. The best way to prevent the FLU is to get vaccinated each year.