Influenza - last updated 15 October 2001 1. Latest data 1.1.
Influenza is one of the infectious diseases that peak during winter.
It peaks at different times in different winters. It is not possible to predict when it will peak, the size of the peak, which age groups will be most affected, or which influenza viruses will be the commonest. Influenza viruses infect the respiratory tract, and cause symptoms including a cold, cough and sore throat but also systemic symptoms such as fever, headache, runny sore eyes and aching muscles. Patients who have systemic symptoms as well as a cold and a cough are described as having flu or flu-like illness because some other viruses cause the same symptoms. Laboratory tests are required to determine the virus that caused illness in individual patients.