Pertussis (Whooping Cough)

Pertussis is a highly contagious respiratory infection caused by the gram-negative bacterium *Bordetella pertussis*. The organism attaches to ciliated respiratory epithelial cells and releases toxins, including pertussis toxin, adenylate cyclase toxin, and tracheal cytotoxin. These toxins disrupt immune signalling, inflame the airway, and injure the cilia that normally move mucus upward. That mechanism explains the distinctive course. The initial catarrhal phase resembles an uncomplicated upper-respiratory infection, so the patient may have rhinorrhea and a mild cough before pertussis is recognized. The patient is highly contagious during this phase. The cough then becomes paroxysmal: repeated forceful coughs are followed by a deep inspiratory whoop, post-tussive vomiting, or—in an infant—a pause in breathing. The airway remains hypersensitive and poorly cleared even after bacterial activity declines, so the cough may persist for weeks or months during convalescence. The “whoop” is not required for recognition. Infants may not generate it because their airways and respiratory reserve are limited; apnea, colour change, poor feeding, or exhaustion may be the first visible signs. Adolescents and adults may also have prolonged cough without a classic whoop.