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 charcoal or cyclodextrin resin for protection from fatty acids and other inhibitory substances. Bordetellae have multiple attachment proteins, including a 69-kDa outer membrane protein (pertactin), filamentous hemagglutinin, and fimbriae. Bordetella pertussis is the only species that expresses the major virulence protein, pertussis toxin. Bordetella pertussis and Bordetella parapertussis are exclusive human pathogens. B. pertussis is the cause of epidemic pertussis and the usual cause of sporadic pertussis. B. parapertussis is an infrequent cause of pertussis in the United States and is genetically more closely aligned with Bordetella bronchiseptica, a common veterinary pathogen causing upper respiratory tract illnesses in animals. Bordetella holmesii, first described as a cause of bronchitis, endocarditis, and septicemia in immunocompromised patients, recently has been documented to cause pertussis-like illnesses. Occasional case reports of B. bronchiseptica in humans include upper and lower respiratory tract illnesses, endocarditis, septicemia, post-traumatic meningitis, and peritonitis. 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 also is a factor.

Epidemiology and clinical manifestations

Pertussis is the only vaccine-preventable disease for which universal immunization is given and the incidence of which continues to rise. The >42 000 cases reported in the United States in 2012 were the highest number reported for any year in the last half century. The actual number of cases is likely to be exponentially greater than that reported, because pertussis is undersuspected, underdiagnosed, and underreported. It was estimated during a prospective vaccine trial in adults that there likely are >600 000 cough illnesses due to B. pertussis in the United States annually. Age-related incidence of pertussis is highest in infants ≤2 months of age (~150 per 100 000), but the greatest number of cases and the reservoirs for B. pertussis are in school-aged children, adolescents, and adults who have waning vaccine immunity and lack the frequent natural subclinical reinfections that boosted immunity in a previous era. Additional factors in resurgence are speculated to include increased awareness, improved diagnostics, use of acellular vaccines for all doses, and pathogen adaptation.