Influenza is a viral infection that affects mainly the nose, throat, bronchi, and occasionally the lungs. The disease usually lasts for about a week, and is characterized by sudden onset of high fever, aching muscles, headache and severe malaise, non-productive cough, sore throat and rhinitis. Most infected people recover within one to two weeks without medical treatment. However, in the very young, the elderly, and those with other serious medical conditions, infection can lead to severe complications of the underlying condition, pneumonia and death.
The virus is transmitted easily via droplets and small particles ejected when infected people cough or sneeze. Influenza tends to spread rapidly in seasonal epidemics.