bronchitis (brŏnkĪˈtĭs) [key], inflammation of the mucous membrane of the bronchial tubes. It can be caused by viral or bacterial infections or by allergic reactions to irritants such as tobacco smoke. The disease is characterized by low-grade fever, chest pains, hoarseness, and productive cough. Acute bronchitis is rarely serious in otherwise healthy adults, but it can be dangerous in infants, children, or adults who suffer from underlying respiratory disease, especially emphysema. It may subside or, particularly with continued exposure to irritants, may persist and progress to chronic bronchitis or pneumonia. The more prolonged chronic bronchitis is frequently secondary to a serious underlying disorder. Chronic bronchitis affected 71,099 persons in the United States in 1986. Cigarette smoking is the risk factor most often associated with chronic bronchitis. Bronchial inflammation can be severe; cough and bronchial spasms are treated with antihistamines, cough suppressants, and bronchodilators. Antibiotics are used if there is evidence of bacterial invasion.