Except for B. avium, all species can cause respiratory disease in humans, although the disease associated with B. pertussis, 'pertussis' or 'whooping cough,' is most severe. B. bronchiseptica has been isolated from infected wounds and from the respiratory tract of humans. The incidence of infections in immunocompromised hosts seems to be increasing. Incidence of whooping cough in the United States had steadily declined since 1950, when vaccine became widely used, leveling at approximately 1900 cases reported annually. An increase has been seen since 1981, however, and more than 4500 cases were reported in 1990.
Fatalities still occur.
Recent epidemiological studies in New York and Wisconsin have shown recovery of B. pertussis from children and adults with respiratory tract disease that does not resemble classical whooping cough. The organism may be more prevalent than currently assumed, since very few laboratories use methods that allow its detection unless requested by a clinician who suspects the disease. Colonies grow within 7 days, appearing small, smooth, convex, with a pearly luster, resembling mercury drops. The colonies are mucoid and tenacious. A Gram stain of the organism reveals minute, faintly staining coccobacilli singly or in pairs.