Pertussis, also known as whooping cough, is caused by infection with the Bordetella pertussis bacteria. The infection is spread through the air by respiratory droplets from an infected person. The incubation period is usually 7 days.

Whooping cough can affect people of any age. Prior to the advent of widespread immunization, the disease occurred mostly in infants and young children. Now that the majority of children are immunized before school age, a higher percentage of cases are seen among adolescents and adults.

About 38% of recognized cases still occur in infants younger than 6 months of age, however. Early immunization (see childhood immunization schedule) can usually prevent the occurrence of this serious disease, which can sometimes be fatal or lead to permanent disability when it affects babies.

The bacteria invade the nose and throat, the breathing tube (trachea), and the lungs. The infection usually lasts 6 weeks. It starts with symptoms similar to the common cold, and progresses to spasms (paroxysms) of coughing after 10 to 12 days.

The cough is characterized by repeated coughing, 2 or 3 coughs without inhaling then a characteristic inspiratory whoop. Typically, the face becomes more red with each cough then subtly bluish (cyanotic).

The child may momentarily lose consciousness at the end of a coughing spell. During this stage, there is heavy mucus production and coughing spells may induce vomiting. Pertussis should always be considered when vomiting is associated with coughing. In infants, choking spells are common.

Recovery begins about four weeks after the onset of symptoms and may take several weeks. Paroxysms of coughing may recur over the next several months, usually due to irritation from an upper respiratory infection.

Immunization may moderate the course of pertussis when it does not produce complete immunity. When symptoms are not classic, pertussis is difficult to diagnose and as a result, the disorder is likely to be underdiagnosed.