Influenza (also known as flu) is a contagious respiratory illness caused by flu viruses. It can cause mild to severe illness, and at times can lead to death. Flu is different from a cold. Flu usually comes on suddenly.
a group of viruses referred to as rhinoviruses. Complications of the common cold include acute bronchitis and pneumonia. People with lung conditions such as asthma and chronic obstructive pulmonary disease are more vulnerable to colds than other people.
