Until recently it was thought that B. pertussis did not invade the tissues. However, recent studies have shown the bacteria to be present in alveolar macrophages. Clinical Features The incubation period of pertussis is commonly 7–10 days, with a range of 4–21 days, and rarely may be as long as 42 days.The clinical course of the illness is divided into three stages.ommunicability Pertussis is highly communicable, as evidenced by secondary attack rates of 80% among susceptible household contacts. Persons with pertussis are most infectious during the catarrhal period and the first 2 weeks after cough onset (i.e., approximately 21 days).