Whooping cough (pertussis) is an upper respiratory infection caused by Bordetella pertussis bacteria. These bacteria live in the saliva and nasal mucus of an infected person. People become infected by inhaling tiny, contaminated droplets from the sneeze or cough of an already infected person.

Once inside the body, pertussis bacteria produce toxins that prevent the respiratory tract from eliminating germs. The bacteria also create chemicals that cause inflammation and damage the lining of breathing passages, specifically the nasopharynx, which is where the nasal passages meet the back of the throat.

People with whooping cough have fits of violent coughing that can leave them gasping for breath. The attempt to inhale quickly through narrowed breathing passages causes the typical, high-pitched “whooping” sound that gives the infection its common name. It appears that the coughing itself is the result of trying to expel thick mucus from the lungs and throat.

Complications of whooping cough may include seizures, stopped breathing (apnea), ear infections and brain damage. In rare cases, whooping cough can be fatal, especially for infants. Secondary bacterial pneumonia is the major cause of these deaths.

Before the vaccine became available, more than 200,000 cases of whooping cough were reported each year, according to the U.S. Centers for Disease Control and Prevention (CDC). Today, that number has been reduced to about 5,000 to 7,000 cases annually.

In the past two decades, there has been a steady increase in the number of new cases of whooping cough, with cyclical spikes every three to five years. Most of these new cases occur in children younger than 6 months, who are not yet fully immunized against the infection. Some physicians are urging new research that will allow earlier vaccinations to protect infants.