The functions of the upper respiratory tract are to move air to and from the lungs, and to filter, moisten, and warm the air. The infections could be caused by viruses or bacteria, and include conditions such as the common cold, influenza, sinus problems, minor sore throat, and so forth. However, because the bronchi are found in the lungs, bronchitis is actually a lower respiratory infection or lung condition. An estimated 10 to 20 percent of the population in the US contract influenza each year. Influenza is characterized by the abrupt onset of fever, muscle aches, sore throat, and a nonproductive cough.
Influenza can make people of any age ill.
Although most people are ill with influenza for only a few days, some have a much more serious illness and may need to be hospitalized. Influenza can also lead to pneumonia and death. A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates for hospitalization and death. Efforts to control the impact of influenza are focused on types A and B. Influenza type C usually causes either a very mild respiratory illness or no symptoms at all. A and B do.