When bronchitis takes a turn for the worse

Chronic bronchitis, a component of chronic obstructive pulmonary disease (COPD), is characterized by a productive cough of sputum on most days for three months in each of two consecutive years with or without impaired airflow obstruction.1 An acute exacerbation of chronic bronchitis (AECB) is defined as a distinct change in baseline cough, sputum, or dyspnea that necessitates an adjustment in management. An AECB often precipitates an exacerbation of COPD and leads to worsening of airflow obstruction. Most patients with chronic bronchitis experience 1.5-3 AECB per year.1,2

Chronic bronchitis and emphysema are the two main components of COPD. In 2001, The National Heart Lung and Blood Institute along with the World Health Organization developed the Global Initiative for Chronic Obstructive Lung Disease (GOLD) to define the severity levels of COPD.1 According to the classification, COPD is airflow limitation that is not fully reversible and is associated with an abnormal and progressive inflammatory response of the lungs to noxious inhaled substances. Emphysema and chronic bronchitis can coexist, making the diagnosis of chronic bronchitis more difficult. Injury in the small airway distinguishes chronic bronchitis from distal alveolar destruction associated with emphysema. 

The diagnosis of COPD should be considered in any patient who has chronic bronchitis or any of the following: shortness of breath, chronic cough, or exposure to risk factors associated with COPD. The diagnosis requires confirmation of airflow obstruction by measuring post-bronchodilator spirometry. A reduction in the forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) indicates an airflow limitation that is not fully reversible. Spirometric severity classification is then useful to guide management and predict mortality.1,2

Risk factors

Risk factors for AECB/COPD include infection, environmental exposures (e.g., dust, allergens), air pollution, medication noncompliance, and continued smoking or exposure to secondhand smoke. Only 15%-20% of smokers develop COPD, indicating an important genetic susceptibility component. Additional risk factors include occupational exposures or exposures to noxious gases, low socioeconomic status, childhood respiratory infection and perinatal events, airway hyperreactivity, and latent adenoviral infection. Teenage smoking or exposure to secondhand smoke may lead to decreased lung function earlier in adulthood.2,3

Most episodes of AECB (80%) are associated with lower respiratory tract infections; 30% are associated with respiratory viruses, and 70% are due to bacterial agents. The most common respiratory viruses are influenza, rhinovirus, and parainfluenza. Aerobic gram-positive bacteria and gram-negative bacteria account for 40%-60% of bacterial infections; Streptococcus pneumoniae, Hemophilus influenzae, and Moraxella catarrhalis are the most common. If patients have been hospitalized or received prior antibiotics, Pseudomonas aeruginosa may be present, and antibiotic resistance may have developed to other bacteria.

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