Bronchitis is a viral respiratory infection that causes inflammation of the lining of the bronchial passages. Symptoms include a persistent cough, coughing up mucus that may be discolored, and fatigue. Bronchitis can last just a few weeks or as long as years and is diagnosed as acute or chronic bronchitis, respectively. Acute bronchitis is common and generally occurs alongside a cold or flu, while chronic bronchitis is more rare and is most commonly a side effect of smoking. You should see a physician if you cough up blood, cannot sleep, have difficulty breathing, have a fever of 100.5 degrees or greater, or if your bronchitis symptoms last longer than three weeks or you are at risk of developing pneumonia. A flu shot may help prevent bronchitis because the condition often accompanies the flu.