What is the etiology of bronchitis?

Tammy is a 33-year-old who presents for evaluation of a cough. She reports that about 3 weeks ago she developed a “really bad cold” with rhinorrhea. The cold seemed to go away but then she developed a profound, deep, mucus-producing cough. Now, there is no rhinorrhea or rhinitis—the primary problem is the cough. She develops these coughing fits that are prolonged, very deep, and productive of a lot of green sputum. She hasn’t had any fever but does have a scratchy throat. Tammy has tried over-the-counter cough medicines but has not had much relief. The cough keeps her awake at night and sometimes gets so bad that she gags and dry heaves. Through and extensive work-up, she is diagnosed with bronchitis.