|Classification and external resources|
This diagram shows acute bronchitis.
|ICD-9||466, 491, 490|
Bronchitis is an inflammation of the mucous membranes of the bronchi (the larger and medium-sized airways that carry airflow from the trachea into the more distal parts of the lung parenchyma). Bronchitis can be divided into two categories: acute and chronic.
Acute bronchitis is characterized by the development of a cough or small sensation in the back of the throat, with or without the production of sputum (mucus that is expectorated, or "coughed up", from the respiratory tract). Acute bronchitis often occurs during the course of an acute viral illness such as the common cold or influenza. Viruses cause about 90% of acute bronchitis cases, whereas bacteria account for about 10%.
Chronic bronchitis, a type of COPD, is characterized by the presence of a productive cough that lasts for three months or more per year for at least two years. Chronic bronchitis usually develops due to recurrent injury to the airways caused by inhaled irritants. Cigarette smoking is the most common cause, followed by exposure to air pollutants such as sulfur dioxide or nitrogen dioxide, and occupational exposure to respiratory irritants. Individuals exposed to cigarette smoke, chemical lung irritants, or who are immunocompromised have an increased risk of developing bronchitis.
Acute bronchitis 
Acute bronchitis is a self-limited infection of the lower respiratory tract causing inflammation of the bronchi. Acute bronchitis is an acute illness lasting less than three weeks with coughing as the main symptom, and at least one other lower respiratory tract symptom such as wheezing, sputum production, or chest pain.
Cough, a common symptom of acute bronchitis, develops in an attempt to expel the excess mucus from the lungs. Other common symptoms of acute bronchitis include: sore throat, shortness of breath, fatigue, runny nose, nasal congestion (coryza), low-grade fever, pleurisy, malaise, and the production of sputum.
Acute bronchitis is most often caused by viruses that infect the epithelium of the bronchi, resulting in inflammation and increased secretion of mucus. Acute bronchitis often develops during an upper respiratory infection (URI) such as the common cold or influenza. About 90% of cases of acute bronchitis are caused by viruses, including rhinoviruses, coronaviruses, adenoviruses, metapneumovirus, parainfluenza virus, respiratory syncytial virus, and influenza. Certain viruses such as rhinoviruses and coronaviruses are also known to cause acute exacerbations of chronic bronchitis. About 10% of cases are caused by bacteria, including Mycoplasma pneumoniae, Chlamydophila pneumoniae, Bordetella pertussis, Streptococcus pneumoniae, and Haemophilus influenzae.
Bronchitis may be diagnosed by a health care provider during a thorough physical examination. Due to the nonspecific signs and symptoms exhibited by individuals with bronchitis, diagnostic tests such as a chest x-ray to rule out pneumonia, a sputum culture to rule out whooping cough or other bacterial respiratory infections, or a pulmonary function test to rule out asthma or emphysema may be used.
Treatment for acute bronchitis is primarily symptomatic. Non-steroidal anti-inflammatory drugs (NSAIDs) may be used to treat fever and sore throat. Even with no treatment, most cases of acute bronchitis resolve quickly.
Most cases of acute bronchitis are caused by viruses, therefore antibiotics are not generally recommended as they are only effective against bacteria. Using antibiotics in cases of viral bronchitis promotes the development of antibiotic-resistant bacteria, which may lead to greater morbidity and mortality. However, even in cases of viral bronchitis, antibiotics may be indicated in certain cases in order to prevent the occurrence of secondary bacterial infections.
Chronic bronchitis 
Chronic bronchitis, a type of chronic obstructive pulmonary disease, is defined by a productive cough that lasts greater than three months each year for at least two years in the absence of other underlying disease. Protracted bacterial bronchitis is defined as a chronic productive cough with a positive bronchoalveolar lavage that resolves with antibiotics.
Symptoms of chronic bronchitis may include wheezing and shortness of breath, especially upon exertion and low oxygen saturations. The cough is often worse soon after awakening and the sputum produced may have a yellow or green color and may be streaked with specks of blood.
Most cases of chronic bronchitis are caused by smoking cigarettes or other forms of tobacco. Additionally, chronic inhalation of air pollution or irritating fumes or dust from hazardous exposures in occupations such as coal mining, grain handling, textile manufacturing, livestock farming, and metal molding may also be a risk factor for the development of chronic bronchitis.
Individuals with an obstructive pulmonary disorder such as bronchitis may present with a decreased FEV1 and FEV1/FVC ratio on pulmonary function tests. Unlike other common obstructive disorders such as asthma or emphysema, bronchitis rarely causes a high residual volume (the volume of air remaining in the lungs after a maximal exhalation effort).
Evidence suggests that the decline in lung function observed in chronic bronchitis may be slowed with smoking cessation. Chronic bronchitis is treated symptomatically and may be treated in a nonpharmacologic manner or with pharmacologic therapeutic agents. Typical nonpharmacologic approaches to the management of COPD including bronchitis may include: pulmonary rehabilitation, lung volume reduction surgery, and lung transplantation. Inflammation and edema of the respiratory epithelium may be reduced with inhaled corticosteroids. Wheezing and shortness of breath can be treated by reducing bronchospasm (reversible narrowing of smaller bronchi due to constriction of the smooth muscle) with bronchodilators such as inhaled long acting β2-adrenergic receptor agonists (e.g., salmeterol) and inhaled anticholinergics such as ipratropium bromide or tiotropium bromide. Mucolytics (also known as expectorants) may have a small therapeutic effect on acute exacerbations of chronic bronchitis. Supplemental oxygen is used to treat hypoxemia (too little oxygen in the blood) and has been shown to reduce mortality in chronic bronchitis patients. Oxygen supplementation can result in decreased respiratory drive, leading to increased blood levels of carbon dioxide (hypercapnea) and subsequent respiratory acidosis.
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- NIH entry on Bronchitis
- MedlinePlus entries on Acute bronchitis and Chronic bronchitis
- Mayo Clinic factsheet on bronchitis