An estimated 10 to 20 percent of the population in the US contract influenza each year. Influenza is a viral infection of the upper respiratory system, which includes the nose, bronchial tubes, and lungs.
Influenza can make people of any age ill.
Although most people and children are ill with influenza for only a few days, some have a much more serious illness and may need to be hospitalized. A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Efforts to control the impact of influenza are focused on types A and B. One of the reasons the flu remains a problem is because the viruses actually alter their structure, exposing adults and children to new types of the virus each time. Influenza type C usually causes either a very mild respiratory illness or no symptoms at all. A and B do.