Acute bronchitis is a short-term respiratory infection that may be referred to as a chest cold. The bronchi branch off the trachea, taking air from the outside into the lungs. In bronchitis, the bronchi become inflamed and produce more mucus.

Bronchi of Lungs
lungs and bronchioles
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In most cases, acute bronchitis is caused by a viral infection. There are times when it may be caused by a bacterial infection.