Which symptom is most distinctive of pertussis?

The symptom most distinctive of pertussis is the paroxysmal cough with crowing inspiration, often referred to as "whooping" cough. This characteristic cough pattern typically involves a series of rapid coughs followed by a high-pitched "whoop" sound as the person attempts to inhale. This signature cough reflects the severe bronchial spasms that occur in pertussis, a contagious respiratory illness caused by the bacterium Bordetella pertussis.

The paroxysmal stage of the cough can lead to exhaustion and vomiting, and the unique sound during the inspiratory phase after coughing results from the narrowing of the airway. The clinical presentation often leads to a definitive diagnosis, as this symptom is not commonly associated with other respiratory conditions.

In contrast, the other choices describe coughs and respiratory sounds that are not specific to pertussis, making them less distinctive as indicators of the disease.