Causes
There are two types of bronchitis:
Acute bronchitis comes on rapidly, usually after a virus has invaded
the upper respiratory tract. Sometimes there is a bacterial infection as well.
Viruses most likely to trigger acute bronchitis are those responsible for influenza
(the flu) or the common cold. The viruses that cause measles and rubella (German
measles) can also cause acute bronchitis. In these cases, it is called acute
infectious bronchitis. The condition is called acute irritative bronchitis
when it is caused by inhaling dust, fumes, or smoke.
Chronic bronchitis is defined as a mucous-producing cough that lasts
for at least three months in two consecutive years. The most important cause
by far is smoking. Exposure to some pollutants can also contribute to chronic
bronchitis. A growing number of specialists believe that some kind of infection
is a necessary final trigger of chronic bronchitis.
About 90% of people with chronic bronchitis are smokers. Certain jobs such
as coal mining, welding, asbetos work and grain handling also increase the risk
of developing bronchitis.