Bronchitis is one of the more common lower respiratory tract infections and may occur in isolation or involve neighboring structures like the trachea or lung tissue (parenchyma). The most common cause of acute bronchitis is an infection while in chronic bronchitis, cigarette smoking is a leading contributing factor.
Acute Bronchitis Causes
Viruses are the most common pathogen implicated in acute infectious bronchitis. A number of viruses including those associated with the seasonal flu (influenza), common cold, and other acute respiratory tract infections (ARTI) like the respiratory syncytial viruses (RSV’s) are the common cause.
Acute bronchitis often develops along with or towards the latter stages of these viral infections which also affects other parts of the respiratory tract – pharyngitis (sore throat), laryngitis and tracheitis. The symptoms of bronchitis typically commence a day or two after the main symptoms of a cold or flu begins as the infections spreads to the lower respiratory tract. The persistent productive cough associated with acute bronchitis may last for 7 to 10 days.
A bacterial infection may occur secondary to a viral respiratory tract infection. It rarely occurs spontaneously, except in smokers, patients with cystic fibrosis, or following aspiration of gastric contents (acid reflux).
Fungal causes of acute infectious bronchitis is also rare and is more likely to occur in an immunocompromised patient (immune deficiency).
This includes a wide range of non-infectious causes, including mechanical, chemical and allergic causes. Depending on the causative factor, it may lead to recurrent episodes of acute bronchitis which can lead to chronic bronchitis.
Some of the causes include :
- Cigarette smoking
- Environment pollution (air)
- Gastroesophageal reflux disease (GERD /acid reflux)
- Organic and inorganic dust
Chronic Bronchitis Causes
Chronic bronchitis is a productive cough lasting 3 months or more and recurring within 2 consecutive years. There is degeneration of the bronchi and the condition is not solely defined by the episodes of bronchial inflammation and mucus hypersecretion.
Repeated episodes of acute bronchitis may lead to chronic bronchitis. Therefore any of the causes mentioned above for acute bronchitis if persistent or recurrent may lead to chronic bronchitis.
However, of these, cigarette smoking and air pollution has been widely implicated. Most long term cigarette smokers suffer with some degree of chronic bronchitis. The same applies for drug users who consume illicit substances through smoking.
GERD, where there is aspiration of the reflux, is now being implicated more frequently in chronic bronchitis as a result of the airway damage by gastric acid. Long-term allergy-related respiratory conditions, especially if poorly managed, may lead to chronic bronchitis due to the thickening of the bronchial walls as a result of persistent inflammation.