Acute bronchitis, also known as a chest cold, is short-term bronchitis – inflammation of the bronchi (large and medium-sized airways) of the lungs. The most common symptom is a cough. Other symptoms include coughing up mucus, wheezing, shortness of breath, fever, and chest discomfort. The infection may last from a few to ten days. The cough may persist for several weeks afterward with the total duration of symptoms usually around three weeks. Some have symptoms for up to six weeks.

In more than 90% of cases, the cause is a viral infection. These viruses may be spread through the air when people cough or by direct contact. Risk factors include exposure to tobacco smoke, dust, and other air pollution. A small number of cases are due to high levels of air pollution or bacteria such as Mycoplasma pneumoniae or Bordetella pertussis. Diagnosis is typically based on a person's signs and symptom. The color of the sputum does not indicate if the infection is viral or bacterial. Determining the underlying organism is typically not needed. Other causes of similar symptoms include asthma, pneumonia, bronchiolitis, bronchiectasis, and COPD. A chest X-ray may be useful to detect pneumonia.

Prevention is by not smoking and avoiding other lung irritants. Frequent hand washing and flu vaccination may also be protective. Treatment of acute bronchitis typically involves rest, paracetamol (acetaminophen), and NSAIDs to help with the fever. Cough medicine has little support for its use and is not recommended in children less than six years of age. Antibiotics should generally not be used. An exception is when acute bronchitis is due to pertussis. Tentative evidence supports honey and pelargonium to help with symptoms.

Acute bronchitis is one of the most common diseases. About 5% of adults are affected and about 6% of children have at least one episode a year. It occurs more often in the winter. More than 10 million people in the United States visit a doctor each year for this condition with approximately 70% receiving antibiotics, most of which are not needed. There are efforts to decrease the use of antibiotics in acute bronchitis.

The primary symptom is a cough with sputum that may be purulent. The illness may also cause shortness of breath or wheezing. Upper respiratory tract infections (URTIs) often precede acute bronchitis, with overlapping symptoms including headache, nasal congestion, and sore throat. About a third of patients will experience a fever, but fevers due to acute bronchitis rarely rise above 100 °F (37.8 °C) or last longer than a few days. As fever and other systemic symptoms are less common in acute bronchitis than in pneumonia, their presence raises suspicion for the latter, especially high or persistent fevers.

Acute bronchitis can be caused by contagious pathogens, most commonly viruses. Typical viruses include respiratory syncytial virus, rhinovirus, influenza, and others. Bacteria are uncommon pathogens but may include Mycoplasma pneumoniae, Chlamydophila pneumoniae, Bordetella pertussis, Streptococcus pneumoniae, and Haemophilus influenzae.

A physical examination will often reveal decreased intensity of breath sounds, wheezing, rhonchi, and prolonged expiration. During examination, physicians rely on history and the presence of persistent or acute onset of cough, followed by a URTI with no traces of pneumonia. Acute bronchitis is typically a clinical diagnosis that relies on patients history and exam, and should be suspected in patients with an acute onset of cough, which often follows a URTI without traces of pneumonia.

Although there is no universally-accepted clinical definition for acute bronchitis, there is a proposed set of practical criteria (Macfarlane, 2001) that include: