Outcome predictors in bronchitis.

A cute bronchitis in previously fit people is a common '*¦*¦ condition often occurring at the time of an upper respiratory tract infection that "goes down onto the chest." Viruses are common etiologic agents, although Mycoplasma pneumoniae may be a frequent cause during epidemics, and recent evidence suggests Chlamydia pneumoniae can also produce this syn¬ drome.1 Secondary bacterial infections may occur due to Streptococcus pneumoniae and nontypable Haemo¬ philus influenzae. Symptoms are relatively mild arid the condition is usually self-limiting, although a con¬ dition of bronchial hyperresponsiveness can develop for weeks after an apparently mild attack. Chronic bronchitis is defined by common consensus as daily production of sputum for at least 3 months in 2 consecutive years. Patients with chronic bronchitis are a heterogeneous group owing to the range of severity of the condition and its common association with airflow obstruction, which may or may not be re¬ versible, and emphysema. Three separate but contin¬ uous entities have been defined: simple chronic bron¬ chitis, chronic or recurrent mucopurulent bronchitis, and chronic obstructive bronchitis.2 Exacerbations are common to all three groups, but their cause may be difficult to identify and might include viral infection, environmental pollutants, allergic responses, and bac¬ terial infection. The cause of an exacerbation may be multifactorial, so that viral infection or levels of air pollution may exacerbate preexisting inflammation in the airways, which in turn may predispose to second¬ ary bacterial infection.3 Understanding the basic mech¬ anisms underlying these events may be germane in predicting the likely outcome of an exacerbation. Pathophysiology The hypersecretion of mucus in chronic bronchitis is due to hypertrophy of the submucosal glands and increase in the numbers of goblet cells in the epithe¬ lium at the expense of ciliated cells. Epithelial meta¬ plasia also occurs, and together with abnormalities of ciliary function and mucus rheology, these changes lead to impairment of mucociliary clearance,4 an important first-line defense mechanism of the airways.