What causes bronchitis?

According to WebMD, bronchitis is an inflammation of the bronchial tubes, which carry air into the lungs. Acute bronchitis is typically caused by a virus; however, it can also be caused by bacteria. It often appears after infections of the upper respiratory tract, such as a cold or the flu.

WebMD notes that symptoms of bronchitis include coughing, as well as tiredness and a mild fever. With bronchitis, a cough can start off dry and then produce mucus after a few days. Symptoms usually last two to three weeks. Pneumonia is a possible complication of bronchitis, in which a patient can develop shortness of breath, high fever, chills and chest or shoulder pain.