Influenza or the flu is a respiratory infection caused by a number of viruses. The viruses pass through the air and enter your body through your nose or mouth. Between 5% and 25% of people in Canada get the flu each year. The flu can be serious or even deadly for elderly people, newborn babies, and people with certain chronic illnesses.
Click here for more information http://www.nlm.nih.gov/medlineplus/flu.html