Chronic bronchitis is a chronic or recurrent cough together with expectoration occurring on most days for at least three months in the year during at least two years. Chronic productive cough followed after some years by the onset of breathlessness is initially episodic and may follow an infection such as influenza or pneumonia; but it later becomes persistent and, after 20 or 30 years with recurrent acute illnesses or exacerbations, respiratory failure ensues and progresses until death with or without congestive heart failure (cor pulmonale).
The many studies of mortality and of morbidity carried out in different countries indicate causative factors operative in both developed and developing countries. Comparing emphysema in different countries has not progressed beyond the confirmation of male preponderance and a relationship to smoking. In relation to chronic obstructive bronchitis, five factors have been identified; three which can be partly quantified and two which do not lend themselves to measurement. The three most significant factors are smoking, air pollution and occupation.