Influenza

Influenza, commonly known as the flu, is an acute respiratory infectious disease caused by influenza viruses. There are different types of influenza, including seasonal flu (prevalent annually in winter, often from November to March), the 2009-2010 H1N1 flu (also known as swine flu), and avian flu. Clinical manifestations are primarily systemic toxic symptoms such as high fever, fatigue, headache, cough, and generalized muscle aches, while respiratory symptoms are relatively mild.