Gram ⊝, obligate aerobic coccobacillus.- Attachment to nasopharyngeal ciliated epithelial cells is via hemagglutinin; pertussis toxin aids in attachment.- Pertussis toxin (A and B component): ADP ribosylation of G_i, thereby impairing it → adenylate cyclase is no longer inhibited → ↑ cAMP → impaired cell signalling.

Stages:- Catarrhal (1-2 weeks): Rhinorrhea, malaise, sneezing, anorexia- Paroxysmal: (2-4 weeks): Repetitive cough with inspiratory whoops, tongue protrusion, cyanosis, posttussive vomiting- Convalescent (3-4 weeks): Deminished paroxysmal cough, development of secondary complications (pneumonia, seizures, encephalopathy)

Diagnosis: Regan-Lowe or Bordet-Genou media, direct immunofluorescence on nasopharyngeal smear, PCR- Blood count: lymphocyte-predominant leukocytosis >50'000 µl that corresponds to disease severity

Treatment: supportive care; erythromycin for 14 days including all household contacts- Prevented by DTaP vaccines; immunity wanes 5-7 years