The incubation period for B. pertussis is the time from exposure and infection until the onset of cough. The incubation period is usually 7-10 days, although it may range from 4-21 days with rare cases as long as 42 days. There are three main stages of the disease:
- Catarrhal stage
- Paroxysmal stage
- Convalescent stage
During the catarrhal stage, the patient generally exhibits a runny nose, sneezing, low-grade fever, and a mild, occasional cough very similar to the common cold. This cough gradually becomes more severe and after a period of 1-2 weeks, the patient enters the paroxysmal stage. A person infected with pertussis is infectious to others from the beginning of the catarrhal stage and up to about three weeks after the cough starts.
The characteristics of the disease are more apparent during the paroxysmal stage. The patient usually has bursts (paroxysms) of numerous, rapid coughs with a final long inspiration, usually accompanied by the characteristic high-pitched whoop sound; hence the name, "whooping cough." When an attack such as this occurs, the patient may become cyanotic (turn blue). Vomiting and exhaustion often follow the episode. The patient usually does not appear ill or display any signs of being ill in between these paroxysmal attacks. This stage of the disease can last from 1-6 weeks. The illness can be milder and the characteristic "whoop" absent in patients who were previously vaccinated.
The patient experiences a gradual recovery during the convalescent stage. The cough usually disappears in 2 to 3 weeks and becomes less paroxysmal in the process. However, coughing spasms often recur with subsequent respiratory infections for many months after the original onset of pertussis.
The table on the following page summarizes the clinical features associated with each stage of pertussis.