Whooping cough is caused by a bacterium called Bordetella pertussis. The bacterium infects the lining of the airways, mainly the windpipe (trachea) and the two airways that branch off from it to the lungs (the bronchi).
When the Bordetella pertussis bacterium comes into contact with the lining of these airways, it multiplies and causes a build-up of thick mucus. It is the mucus that causes the intense bouts of coughing as your body tries to expel it.
The bacterium also causes the airways to inflame (swell up), making them narrower than usual. As a result, breathing is made difficult, which causes the 'whoop' sound as you gasp for breath after a bout of coughing.
How whooping cough spreads
Whooping cough is most infectious during the early stages of the condition. The Bordetella pertussis bacterium is carried in droplets of moisture in the air. When someone with whooping cough sneezes or coughs, they propel hundreds of infected droplets into the air. If the droplets are breathed in by someone else, the bacterium will infect their airways.
How to avoid passing on the infection
Whooping cough is highly infectious, so if you or your child have it, it is very important to stay away from others until the bacterium has completely cleared.
The affected person should stay at home until they have:
- completed a course of antibiotics from their GP or
- had intense bouts of coughing (paroxysms) for three weeks
Although bouts of coughing may continue after three weeks, it is unlikely that you will still be infectious because the bacterium will have gone.
See Whooping cough – treatment for more information about antibiotics for whooping cough.
