Influenza, more commonly known as the flu, is a viral illness that affects the respiratory tract.

What is going on in the body?

There are 3 types of influenza viruses: influenza A, B, and C. Each of these has several subtypes. All these forms of the virus mutate (change their genes slightly) and vary from year to year. This is why it is possible for the same person to have repeated episodes of the flu. Flu is usually transmitted from person to person through drops of respiratory discharge.

What are the causes and risks of the infection?

The flu strikes about 7 out of 1,000 people. It is highly contagious. Flu is much more common among people who live in institutional settings such as nursing homes. Those who come in contact with many other people in schools, day care centers, or large group organizations are also more likely to become infected.

The flu season usually begins in late October or early November and goes through the early spring. The number of cases peaks in January and February.