Merck Manual

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Acute Bronchitis


Sanjay Sethi

, MD, University at Buffalo SUNY

Last full review/revision Mar 2020| Content last modified Mar 2020
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Acute bronchitis is inflammation of the tracheobronchial tree, commonly following an upper respiratory infection, that occurs in patients without chronic lung disorders. The cause is almost always a viral infection. The pathogen is rarely identified. The most common symptom is cough, with or without fever, and possibly sputum production. Diagnosis is based on clinical findings. Treatment is supportive; antibiotics are usually unnecessary. Prognosis is excellent.

Acute bronchitis is frequently a component of an upper respiratory infection (URI) caused by rhinovirus, parainfluenza, influenza A or B virus, respiratory syncytial virus, coronavirus, or human metapneumovirus. Bacteria, such as Mycoplasma pneumoniae, Bordetella pertussis, and Chlamydia pneumoniae, cause less than 5% of cases; these sometimes occur in outbreaks.

Acute inflammation of the tracheobronchial tree in patients with underlying chronic bronchial disorders (eg, chronic obstructive pulmonary disease [COPD], bronchiectasis, cystic fibrosis) is considered an acute exacerbation of that disorder rather than acute bronchitis. In these patients, the etiology, treatment, and outcome differ from those of acute bronchitis.

Pearls & Pitfalls

  • Acute cough in patients with COPD, bronchiectasis, or cystic fibrosis should typically be considered an exacerbation of that disorder rather than simple acute bronchitis.

Symptoms and Signs

Symptoms are a nonproductive or mildly productive cough accompanied or preceded by URI symptoms, usually by > 5 days. Subjective dyspnea results from chest pain or tightness with breathing, not from hypoxia.

Signs are often absent but may include scattered rhonchi and wheezing. Sputum may be clear, purulent, or occasionally contain blood. Sputum characteristics do not correspond with a particular etiology (ie, viral vs bacterial). Mild fever may be present, but high or prolonged fever is unusual and suggests influenza or pneumonia.

On resolution, cough is the last symptom to subside and often takes 2 to 3 weeks or even longer to do so.


  • Clinical evaluation

  • Sometimes chest x-ray to exclude other disorders

Diagnosis is based on clinical presentation. Testing is usually unnecessary. However, patients who complain of dyspnea should have pulse oximetry to rule out hypoxemia. Chest x-ray is done if findings suggest serious illness or pneumonia (eg, ill appearance, mental status change, high fever, tachypnea, hypoxemia, crackles, signs of consolidation or pleural effusion). Older patients are the occasional exception, as they may have pneumonia without fever and auscultatory findings, presenting instead with altered mental status and tachypnea.

Sputum Gram stain and culture usually have no role. Nasopharyngeal samples can be tested for influenza and pertussis if these disorders are clinically suspected (eg, for pertussis, persistent and paroxysmal cough after 10 to 14 days of illness, only sometimes with the characteristic whoop and/or retching, exposure to a confirmed case). Viral panel testing is not usually recommended because results do not affect treatment.

Cough resolves within 2 weeks in 75% of patients. Patients with persistent cough should undergo a chest x-ray. The decision to evaluate for noninfectious causes, including postnasal drip and gastroesophageal reflux disease, can usually be made on the basis of the clinical presentation. Differentiation of cough-variant asthma may require pulmonary function testing.


  • Symptom relief (eg, acetaminophen, hydration, possibly antitussives)

  • Inhaled beta-agonist for wheezing

Acute bronchitis in otherwise healthy patients is a major cause of antibiotic overuse. Nearly all patients require only symptomatic treatment, such as acetaminophen and hydration. Evidence supporting efficacy of routine use of other symptomatic treatments, such as antitussives, mucolytics, and bronchodilators, is weak. Antitussives should be considered only if the cough is interfering with sleep. Patients with wheezing may benefit from an inhaled beta2-agonist (eg, albuterol) for a few days. Broader use of beta2-agonists is not recommended because adverse effects such as tremor, nervousness, and shaking are common.

Though modest symptomatic benefits occur with antibiotic use in acute bronchitis, the self-limiting nature of acute bronchitis and the risk of adverse effects and antibiotic resistance argue against widespread antibiotic use. Oral antibiotics are typically not used except in patients with pertussis or during known outbreaks of bacterial infection. A macrolide such as azithromycin 500 mg orally once, then 250 mg orally once a day for 4 days or clarithromycin 500 mg orally twice a day for 7 days is given.

Pearls & Pitfalls

  • Treat most cases of acute bronchitis in healthy patients without using antibiotics.

Key Points

  • Acute bronchitis is viral in > 95% of cases, often part of an upper respiratory infection.

  • Diagnose acute bronchitis mainly by clinical evaluation; do chest x-ray and/or other tests only in patients who have manifestations of more serious illness.

  • Treat most patients only to relieve symptoms.

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