Bordetellae are fastidious, non–carbohydrate-fermenting, tiny, gram-negative coccobacilli that grow aerobically on starch blood agar or synthetic medium supplemented with nicotinamide and amino acids for growth and char-coal or cyclodextrin resin for protection from fatty acids and other inhibitory substances. Bordetellae have multiple attachment proteins, including a 69-kd outer membrane protein (pertactin), filamentous hemagglutinin, and fimbriae. Bordetella pertussis is the only species that expresses the major virulence protein, pertussis toxin. Bordetella pertussis is an exclusive human pathogen that is the sole cause of epidemic pertussis and the usual cause of sporadic pertussis. Bordetella parapertussis is an infrequent cause of pertussis and is genetically more closely aligned with Bordetella bronchiseptica, a common veterinary pathogen causing upper respiratory tract illnesses in animals. Other Bordetella species do not cause pertussislike illnesses. Occasional case reports of B. bronchiseptica in humans include upper and lower respiratory tract illnesses, endocarditis, septicemia, post-traumatic meningitis, and peritonitis. Bordetella holmesii and B. holmesii-like organisms have occasionally caused bronchitis, endocarditis, septicemia, and respiratory failure. Bordetella hinzii has caused bloodstream infection in a handful of cases, associated usually with pulmonary symptoms. Asplenia or immunosuppression has been present in many adults infected with Bordetella non-pertussis and non-parapertussis species. Exposure to pets is also a factor.