Influenza, or ‘flu’, is a common upper respiratory tract infection caused by the influenza virus. However, many other viruses can present with similar symptoms and signs of a ‘flu-like’ illness. Influenza usually occurs in epidemics. These may be very serious and cause many deaths. Like the common cold, the influenza virus is spread by coughing, sneezing and direct hand-to-hand contact. Influenza usually presents 1 to 3 days after infection.
As is difficult to clinically tell whether a patient is infected with the influenza virus or another virus, such as rhinovirus, it is better to speak of a flu-like illness unless there is a proven epidemic of influenza infections at the time.