What causes bronchitis?

The viruses that cause the common cold or flu (influenza viruses A and B) usually cause bronchitis, but bacteria (e.g. Mycoplasma pneumoniae) can sometimes also cause it.

Other viruses that cause bronchitis include the parainfluenza viruses (which can also cause croup and bronchiolitis), the respiratory syncytial virus (which can also cause bronchiolitis), the coronaviruses (which can also cause colds) and the adenoviruses (which can also cause colds, pneumonia and croup).

The viruses that cause respiratory tract infections such as bronchitis are usually spread when someone infected with the virus sneezes or coughs, releasing droplets that contain the virus into the air. These droplets can be breathed in by others, or transferred to anyone who touches a surface contaminated with droplets containing the virus.

Some people are at more risk of getting bronchitis and of having more severe symptoms including people who:

  • are older
  • smoke
  • have a weakened immune system (e.g. due to HIV or some medicines)
  • are exposed to chemicals that can irritate the lung tissue (e.g. in their workplace).

Find out more about the symptoms, diagnosis, and treatment of bronchitis.

  • Respiratory Expert Group. Therapeutic guidelines: Respiratory; Acute bronchitis. Melbourne: Therapeutic Guidelines Ltd; March 2012.