The term 'cold-weather illness' can refer to the FLU, which is a contagious respiratory illness caused by the influenza virus. It is characterized by fever, sore throat, muscle aches, and fatigue. Symptoms can range from mild to severe and can last up to two weeks. The FLU is spread through contact with an infected person or through contact with contaminated surfaces. Vaccination is the best way to prevent the FLU.