Acute bronchitis is one of the most common conditions encountered in clinical practice. It is a self-limited inflammation of the bronchi due to upper airway infection. Patients with acute bronchitis present with a cough lasting more than five days (typically one to three weeks), which may be associated with sputum production. Acute bronchitis should be distinguished from chronic bronchitis, a condition in patients with chronic obstructive pulmonary disease distinguished by a cough for at least three months in each of two successive years. (See "Chronic obstructive pulmonary disease: Definition, clinical manifestations, diagnosis, and staging", section on 'Definitions'.)
This respiratory condition is generally caused by a virus. However, reports indicate that more than 60 to 90 percent of patients with acute bronchitis who seek care are given antibiotics [1-4]. Additionally, 75 percent of all antibiotic prescriptions are written for upper respiratory infections .
Guidelines from the American College of Physicians  and the Centers for Disease Control and Prevention (CDC)  are intended to dissuade clinicians from prescribing antibiotics for acute bronchitis . Both guidelines state unequivocally that pertussis is the only indication for antibacterial agents in the treatment of acute bronchitis. However, the frequency of prescriptions for antibiotics for acute bronchitis has decreased only modestly, from approximately 75 to 60 percent in over 10 years from guideline distribution . Additionally, the choice of antibiotics prescribed for the treatment of acute bronchitis has changed substantially during the same time span. Prior to 1990, approximately 20 percent of antibiotics prescribed for the treatment of acute bronchitis were broad spectrum; more recently, approximately 60 percent of all prescriptions written for this condition were for broad-spectrum agents [8,9].
Acute bronchitis caused by microbial infection will be reviewed here. Exacerbations of chronic bronchitis and treatment of viral upper respiratory infections are discussed separately. (See "Management of infection in acute exacerbations of chronic obstructive pulmonary disease" and "The common cold in adults: Treatment and prevention".)
The usual causes of acute bronchitis are viral infections of the upper airways including influenza A and B, parainfluenza, coronavirus (types 1-3), rhinovirus, respiratory syncytial virus, and human metapneumovirus . Several case series examined the etiology of acute bronchitis in patients without underlying lung disease [11,12]. An etiologic agent was established in a minority of cases (29 percent of 42 episodes in one study , 16 percent of 113 patients in another ); viruses were the most common agents identified in both studies.