text: what causes bronchitis? answer to causes of bronchitis acute bronchitis is usually caused by a virus. it is more common during the winter months, and you often develop it after having an upper respiratory tract illness such as influenza (flu) or a cold. respiratory syncytial virus (rsv) may be a cause, especially in adults older than 65. acute bronchitis is caused by bacteria about 10% of the time.  acute bronchitis can also be caused by exposure to smoke, chemicals, or air pollution, all of which can irritate the bronchial tubes, or it can develop from accidentally inhaling (aspirating) food, vomit, or mucous material.