The disease usually starts five to 21 days after exposure to the bacterium. Initial symptoms include cold-like symptoms and maybe a mild cough or fever. In babies, the cough can be minimal or even not present. In its early stages, pertussis appears to be nothing more than a common cold, so it is often not suspected or diagnosed until more severe symptoms appear.
The bacteria attach to the cilia (tiny, hair-like extensions) that line part of the upper respiratory system. The bacteria release toxins (poisons) that damage the cilia, causing the airways to swell, leading to difficulty breathing.
As the disease progresses over the course of a week or two, the traditional symptoms of pertussis may appear. Pertussis can cause violent and rapid coughing, over and over, until the air is gone from the lungs causing a loud "whooping" sound on inhalation. The whoop is not present in all cases. Sometimes the extreme coughing fits (called paroxysm) are followed by episodes of vomiting. These coughing fits make it hard to eat, drink, breathe, and, as they are more pronounced at night, to sleep. However, in-between episodes, the person seems well. The coughing fits become more common and worsen as the illness continues, sometimes for many weeks or months. The prolonged cough is associated with the toxin that was produced by the bacteria. Even if antibiotics are prescribed to kill the bacteria, the cough may persist.
Pertussis is most dangerous for babies. Babies may have a symptom known as apnea. Apnea is a pause in the child's breathing pattern. Babies are at greatest risk for pertussis-related complications and mortality. Death is infrequent and most likely to occur in unvaccinated infants.
Listen to an example of pertussis